WO2012059904A1

WO2012059904A1 - A wireless trackable device, and a system and a method for determining the spatial location of an individual

Info

Publication number: WO2012059904A1
Application number: PCT/IE2011/000058
Authority: WO
Inventors: Liam Thomas Darling; Michael Andrew Dunne
Original assignee: San Central Limited
Priority date: 2010-11-03
Filing date: 2011-11-03
Publication date: 2012-05-10

Abstract

A system (1) for tracking a subject in a compound (2) comprises a plurality of fixed position transmitters (7) which continuously transmit a signal in ZIGBEE format indicative of their respective spatial locations. A wireless trackable device (10) is attached to a subject for determining the spatial location of the subject and for transmitting a signal indicative of the location of the subject to a base tracking station (12). The wireless trackable device (10) comprises a first wireless receiver (18) adapted for receiving signals from a satellite GPS system indicative of the location of the trackable device (10). A second wireless receiver (19) in the wireless trackable device (10) receives signals from the fixed position transmitters (7). A microprocessor (20) in the trackable device (10) determines the wireless receiver (18,19), the strength of the received signals of which is strongest and determines the position of the trackable device (10) from signals received from that wireless receiver (18,19). A transmitter (21) in the trackable device (10) transmits the current position of the trackable device (10) for reception by the base tracking station (12) together with a unique identity code of the trackable device in ZIGBEE format.

Description

"A wireless trackable device, and a system and a method

for determining the spatial location of an individual"

The present invention relates to a wireless trackable device, and the invention also relates to a system and a method for tracking an individual and for determining the spatial location of the individual.

Wireless trackable devices are known, and are commonly used for tracking the movements of human and animal subjects, and in particular, for tracking the movement of children. In general, such wireless trackable devices are mobile phone based devices or GPS based devices, and are attached to the subject to be tracked. These trackable devices determine their position, and in turn the position of the subjects to which they are attached by triangulation using signals received from telecommunications masts of a mobile phone telecommunications network, or in the case of GPS based devices using signals received from GPS satellites. The spatial locations of such masts are known, which in turn allows such trackable devices to determine their spatial locations by triangulation using signals received from the masts. Periodically or on receiving an activation signal from a remote base tracking station, such trackable devices relay their current position to the base tracking station. The current position, in general, is relayed from the trackable device to the base tracking station as a text message which is transmitted over the mobile phone telecommunications network or as an encoded signal which is transmitted by a radio transmitter. Similarly, the activation signal from the base tracking station to the trackable device to activate the trackable device to transmit its current position is transmitted from the base tracking station to the trackable device as a text message over the mobile phone telecommunications network or as an encoded signal which is transmitted by a radio transmitter.

These known trackable devices suffer from a number of disadvantages. A particularly serious disadvantage of such known trackable devices which are mobile phone based devices or GPS based devices is that if the subject to which the trackable device is attached moves into a location of poor coverage by the mobile phone telecommunications network or the GPS system on which the trackable device is supported, or a location of no coverage by the mobile phone

telecommunications network or GPS system, two problems arise, firstly, the trackable device is incapable of determining its position due to the absence or poor quality, as the case may be, of the signal available in the location, and secondly, because of the absence or poor quality, as the case may be, of the available signal of the mobile phone telecommunications network, the trackable device is incapable of transmitting its current position. These are serious disadvantages, particularly where the device is being used to track the movements of a child. It is well known that mobile phone telecommunications network signals are commonly absent or particularly weak in mountainous areas, built-up areas in which the buildings are relatively tall. It is also well known that GPS signals from GPS satellites are unavailable or relatively weak in areas where a clear view of the sky is obstructed. Additionally, in such built-up areas, while the mobile phone

telecommunications network signal or the GPS signal may be adequate outside such buildings, the signals may be absent or inadequate within such buildings, and thus, if a subject being tracked moves into such a building in which the mobile phone telecommunications network signal or GPS signal is absent or inadequate, tracking of such a subject is impossible.

A further problem with such known trackable devices which are mobile phone based devices is that the accuracy based on mast triangulation can be questionable, and can result in relatively large errors in the computation of the spatial location of the trackable device.

A further problem with such trackable devices which are mobile phone based devices is that a cost is incurred each time the trackable device relays its position to the base tracking station, and also each time the base tracking station transmits an activation signal to the trackable device.

There is therefore a need for a wireless trackable device which addresses at least some of the problems of such known wireless trackable devices, and there is also a need for a system and a method for tracking a subject which addresses at least some of the problems of such known wireless trackable devices.

The present invention is directed towards providing a wireless trackable device. The invention is also directed towards providing a system for tracking a human or animal subject, and the invention is further directed towards providing a method for tracking a human or animal subject.

According to the invention there is provided a wireless trackable device comprising a first communicating means adapted for wirelessly communicating with a satellite global positioning system (GPS), a second communicating means adapted for wirelessly communicating with at least one land based wireless transmitter of known spatial location, a comparing means adapted for comparing the strength of signals received by the first and second communicating means with each other and for producing a select signal indicative of the one of the first and second communicating means, the strength of the received signals of which is strongest, a signal processing means adapted for determining the spatial location of the trackable device from signals read from the first and second communicating means, the signal processing means being responsive to the select signal from the comparing means for determining the spatial location of the trackable device from signals read from the one of the first and second communicating means, the strength of the received signals of which is strongest and for producing a signal indicative of the spatial location of the trackable device, and a transmitting means for wirelessly transmitting the signal indicative of the spatial location of the trackable device for reception by a tracking station.

Preferably, the first communicating means comprises a first wireless receiver.

Advantageously, the first communicating means is adapted for receiving signals from at least one satellite of the satellite GPS system, and preferably, from at least three satellites of the satellite GPS system. Ideally, the first communicating means is adapted for receiving signals from four satellites of the GPS system.

In one aspect of the invention the second communicating means comprises a second wireless receiver. Preferably, the second communicating means is adapted for receiving signals from a plurality of the land based wireless transmitters of respective known spatial locations spaced apart from each other. Advantageously, the second communicating means is adapted for receiving signals from the respective land based wireless transmitters in ZIGBEE format.

Preferably, the signal processing means is adapted for determining the location of the trackable device as a function of latitude and longitude co-ordinates of the earth. Advantageously, the signal processing means is adapted for determining the location of the trackable device from the strength of signals received from at least one land based wireless transmitter. Ideally, the signal processing means is adapted for determining the location of the trackable device from the strength of signals received from two land based wireless transmitters.

In another aspect of the invention the signal processing means comprises a first signal processing means for determining the location of the trackable device from signals received by the first communicating means from the at least one satellite of the satellite GPS system. Preferably, the first signal processing means is adapted for determining the location of the trackable device from signals of at least three satellites of the satellite GPS system by a triangulation method.

In a further aspect of the invention the signal processing means comprises a second signal processing means for determining the location of the trackable device from signals received from the at least one land based wireless transmitter. Preferably, the second signal processing means is adapted for determining the location of the trackable device from signals received from at least two land based wireless transmitters by a triangulation method.

In another aspect of the invention the transmitting means is adapted for transmitting the signal indicative of the spatial location of the trackable device in ZIGBEE format.

Preferably, the trackable device comprises a housing, which ideally is a waterproof housing. Advantageously, the first and second communicating means, the comparing means, the signal processing means and the transmitting means are located in the housing.

In another aspect of the invention a means for attaching the trackable device to an individual human or animal subject is provided. Preferably, the means for attaching the trackable device to an individual human or animal subject is adapted for attaching to a human subject.

In one aspect of the invention the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to a wrist of a human subject. In an alternative aspect of the invention the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to an ankle of a human subject.

Preferably, the means for attaching the trackable device to an individual human or animal subject comprises a strap. Alternatively, the means for attaching the trackable device to a human or animal subject comprises a lanyard extending from the trackable device and adapted so that the trackable device is wearable as a pendant. In another aspect of the invention a detecting means is provided for detecting one of removal of the trackable device from a human or animal subject and loosening of the trackable device from the human or animal subject. Preferably, the signal processing means is adapted to monitor the detecting means in order to detect the one of removal of the trackable device from the human or animal subject or the loosening of the trackable device from the human or animal subject.

Advantageously, the signal processing means is responsive to a signal from the detecting means indicative of one of removal of the trackable device from the human or animal subject and loosening of the trackable device from the human or animal subject for producing an alarm signal and for operating the transmitting means to transmit the alarm signal indicative of removal or loosening of the trackable device from the human or animal subject. Ideally, the alarm signal produced by the signal processing means indicative of removal or loosening of the trackable device from the human or animal subject comprises a data signal indicative of the spatial location of the trackable device.

In a further aspect of the invention the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside a predefined area for producing an alarm signal. Preferably, the alarm signal produced by the signal processing means in response to the determined spatial location of the trackable device being indicative of a location outside the predefined area comprises a data signal indicative of the spatial location of the trackable device. Advantageously, the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside the predefined area for operating the transmitting means to transmit the alarm signal.

In a further aspect of the invention the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in a predefined location for more than a predefined time period for producing an alarm signal. Preferably, the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in the predefined location for more than a predefined time period for operating the transmitting means to transmit the alarm signal.

Advantageously, the alarm signal comprises a data signal indicative of the location of the trackable device.

The invention also provides a system for tracking a human or animal subject, the system comprising at least one land based wireless transmitter of known spatial location, a trackable device according to the invention adapted for attaching to the human or animal subject, and a tracking station for reading signals transmitted by the trackable device indicative of the spatial location of the trackable device.

Additionally the invention provides a system for tracking a human or animal subject, the system comprising at least one land based wireless transmitter of known spatial location, a wireless trackable device adapted for attaching to the human or animal subject, the wireless trackable device comprising a first communicating means adapted for wirelessly communicating with a satellite global positioning system (GPS), a second communicating means adapted for wirelessly communicating with the at least one land based wireless transmitter of known spatial location, a comparing means adapted for comparing the strength of signals received by the first and second communicating means with each other and for producing a select signal indicative of the one of the first and second communicating means, the strength of the received signals of which is strongest, a signal processing means adapted for determining the spatial location of the trackable device from signals read from the first and second communicating means, the signal processing means being responsive to the select signal from the comparing means for determining the spatial location of the trackable device from signals read from the one of the first and second communicating means, the strength of the received signals of which is strongest and for producing a signal indicative of the spatial location of the trackable device, and a transmitting means for wirelessly transmitting the signal indicative of the spatial location of the trackable device, and a tracking station for remotely reading the signals transmitted by the trackable device which are indicative of the spatial location of the trackable device.

Preferably, a plurality of land based wireless transmitters are provided spaced apart from each other, each land based wireless transmitter being of known spatial location. Advantageously, each land based wireless transmitter is adapted for transmitting a signal indicative of its spatial location. Ideally, each land based wireless transmitter is adapted for transmitting a signal indicative of its GPS position.

In one aspect of the invention the signal transmitted by each land based wireless transmitter is indicative of the spatial location of the land based wireless transmitter produced as a function of the latitude and longitude co-ordinates of the spatial location of the land based wireless transmitter. Preferably, each land based wireless transmitter is adapted for transmitting the signal indicative of the spatial location thereof in a ZIGBEE format.

Further the invention provides a method for tracking a human or animal subject, the method comprising providing at least one land based wireless transmitter of known spatial location, attaching a wireless trackable device to the human or animal subject, the wireless trackable device being provided with a first wireless

communicating means adapted for communicating with a satellite global positioning system, a second wireless communicating means adapted for communicating with the at least one land based wireless transmitter, a comparing means adapted for comparing the strength of signals received by the first and second communicating means with each other and for producing a select signal indicative of the one of the first and second communicating means, the strength of the received signals of which is strongest, a signal processing means adapted for determining the spatial location of the trackable device from signals read from the first and second communicating means, the signal processing means being responsive to the select signal from the comparing means for determining the spatial location of the trackable device from signals read from the one of the first and second communicating means, the strength of the received signals of which is strongest and for producing a signal indicative of the spatial location of the trackable device, and a transmitting means for wirelessly transmitting the signal indicative of the spatial location of the trackable device, and remotely reading the signal from the trackable device which is indicative of the spatial location of the device to determine the location of the human or animal subject. Preferably, a tracking station is provided for remotely reading the signals transmitted by the trackable device which are indicative of the spatial location of the trackable device. Advantageously, the tracking station receives the signals indicative of the spatial location of the trackable device in a ZIGBEE format. The advantages of the invention are many. A particularly important advantage of the invention is that the wireless trackable device is capable of tracking the movement of a subject even in areas where the signal of a satellite GPS system is absent or of sufficiently poor quality to prevent the wireless trackable device determining its location from the satellite global positioning system. Accordingly, as a subject moves between areas of poor coverage or areas where coverage of a satellite GPS system is absent, the movement of the subject can be tracked. This results from the fact that the wireless trackable device according to the invention is capable of receiving signals from both a satellite global positioning system and from land based masts of known spatial location which are located in areas where coverage of a satellite global positioning system is poor or absent. A particularly important advantage of the invention is achieved when the land based masts of known spatial location are adapted to transmit signals indicative of their position in ZIGBEE format. One advantage of providing the masts of the known spatial locations to transmit signals of their respective positions in ZIGBEE format is that ZIGBEE is a relatively low cost system and minimises battery usage. In particular, ZIGBEE has in-built redundancy, and if the transmitter of one mast fails, signals from a transmitter on an adjacent mast can take over. A further important advantage of the invention is achieved when the transmitter of the wireless trackable device is adapted to transmit the position of the wireless trackable device in the form of a ZIGBEE format signal, since ZIGBEE minimises battery usage. Since the spatial locations of the trackable device according to the invention are transmitted in ZIGBEE format by the transmitter of the trackable device, no transmission costs are incurred as in the case of mobile phone based devices. This, thus, minimises the cost of using the wireless trackable device, since the wireless trackable device can transmit its current location for reception by the base tracking station at no cost.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, which is given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic plan view of a system according to the invention for tracking a human or animal subject,

Fig. 2 is a side elevational view of a wireless trackable device also according to the invention of the system of Fig. 1 ,

Fig. 3 is a top plan view of the trackable device of Fig. 2, and

Fig. 4 is a block representation of circuitry of the trackable device of Fig. 2. Referring to the drawings, there is illustrated a system according to the invention, indicated generally by the reference numeral 1 , for tracking one or more human or animal subjects, typically children, in a relatively large compound 2, in which many people congregate, and in particular in which many children congregate, such as a theme park, a holiday camp, a large playground or the like. Such compounds as the compound 2 typically comprise a perimeter boundary wall or fence, and more typically a boundary wall 4, and one or more buildings 5, and typically a number of buildings 5 which are freely accessible to children from the compounds. The area of such compounds may be of any area but typically would range from as low as five acres and lower up to 50 square miles and greater.

The system 1 according to the invention comprises a plurality of spaced apart land based wireless transmitting means of known spatial location, which in this embodiment of the invention are provided by fixed position transmitters 7 which are configured to continuously at predefined millisecond intervals of approximately 250 milliseconds transmit a signal in ZIGBEE format indicative of their respective spatial locations. In this embodiment of the invention a number of the fixed position transmitters 7 are located in each building 5, and a number of the fixed position transmitters 7 are also located in the grounds of the compound 2. Typically, at least two fixed position transmitters 7 are located in each room of each building 5. In this embodiment of the invention the specific location of each fixed position transmitter 7 is pre-programmed into the fixed position transmitter 7 as its latitude and longitude co-ordinates using GPS format. Thus, each fixed position transmitter 7 continuously at the predefined millisecond intervals transmits a signal indicative of its spatial location based on GPS latitude and longitude co-ordinates.

The system 1 also comprises a wireless trackable device, which is also according to the invention and is indicated generally by the reference numeral 10. The trackable device 10 is adapted for attaching to the wrist of a child. The trackable device 10 is adapted to determine its spatial location within the compound 2 and to transmit a signal indicative of its location for reception by a tracking station 12 which may be located within or externally of the compound 2, but in this embodiment of the invention is located within the compound 2. In this embodiment of the invention a plurality of trackable devices 10 are provided for attaching to respective children for transmitting the signals indicative of the location of the respective children to the tracking station 12. The trackable devices 10 are similar to each other, and for convenience only one of the trackable devices 10 is illustrated in the compound 2 of Fig. 1.

Each trackable device 10 comprises a waterproof housing 14 of plastics material, see Figs. 2 and 3. A means for attaching the trackable device 10 to the wrist of a child comprises a bracelet strap 15 of plastics, rubber or leather material extending from the housing 14, and a clasp 16 on the strap 15 releasably secures the strap 15 around the wrist of the child.

Referring now to Fig. 4, each trackable device 10 comprises a first communicating means, namely, a first wireless receiver 18 which is located in the housing 14, and which is adapted for communicating with a satellite GPS system and for receiving signals from satellites of the satellite GPS system indicative of the GPS locations of the satellites based on the respective GPS latitude and longitude co-ordinates of the satellites, from which the trackable device 10 computes its spatial location. A second communicating means, namely, a second wireless receiver 19 is located in the housing 14, and is adapted for receiving signals in ZIGBEE format from adjacent ones of the fixed position transmitters 7, from which the trackable device 10 also computes its spatial location.

A signal processing means, which in this embodiment of the invention comprises a microprocessor 20 is located in the housing 14 and is programmed to act as a comparing means, and at the predefined millisecond time intervals compares the strength of the signals received by the first and second receivers 18 and 19 with each other, in order to ascertain which of the first and second receivers 18 and 19 is receiving the strongest signal. The microprocessor 20 is programmed to compare the amplitudes of the signals received from the satellite GPS system and the fixed position transmitters 7 by the first and second receivers 18 and 19, respectively, in order to determine which of the receivers 18 and 19 is receiving the strongest signal. The microprocessor 20 is programmed to determine the spatial location of the trackable device 10 at the predefined millisecond intervals from the signals received by the one of the first and second receivers 18 and 19, the received signals of which is determined as being the strongest.

On determining the location of the trackable device 10, the microprocessor 20 is programmed to produce a signal indicative of the location of the trackable device 10 based on the GPS latitude and longitude co-ordinates of the location of the trackable device 10. The microprocessor 20 then operates a wireless transmitter 21 , which is also located in the housing 14 to output the signal indicative of the spatial location of the trackable device 10 for reception by the tracking station 12. The transmitter 21 is a ZIGBEE transmitter and transmits the signal indicative of the spatial location of the trackable device 10 in ZIGBEE format over standard internet protocol.

The microprocessor 20 in acting as the comparing means for comparing the strengths of the signals received by the first and second receivers 18 and 19, respectively, produces a select signal indicative of the one of the first and second receivers 18 and 19, the strength of the received signals of which is strongest. The microprocessor 20 is programmed to be responsive to the select signal to read the signals from the one of the first and second receivers 18 and 19, the strength of the received signals of which is strongest, and in turn to determine the location of the trackable device 10 from those read signals.

When the microprocessor 20 is determining the spatial location of the trackable device 10 from the signals read from the first receiver 18 which have been received from satellites of the satellite GPS system, the microprocessor 20 reads the GPS latitude and longitude co-ordinates of at least three satellites, and preferably four satellites of the GPS system. The microprocessor 20 is programmed to determine the spatial location of the trackable device 10 based on GPS latitude and longitude co-ordinates from the signals received from the satellites of the GPS system. The microprocessor 20 produces a data signal indicative of the latitude and longitude co- ordinates of the spatial location of the trackable device 10. The data signal indicative of the spatial location of the trackable device 10 is then packaged into a transmittable package which comprises data including a unique identity code which identifies the specific trackable device 10 and the GPS longitude and latitude co- ordinates of the location of the trackable device 10. The packaged data produced by the microprocessor 20 is time and date stamped, and then transmitted by the transmitter 21 in ZIGBEE format over standard internet protocol at the predefined millisecond intervals of approximately 250 milliseconds for reception by the tracking station 12.

When the microprocessor 20 is determining the spatial location of the trackable device 10 from signals read from the second receiver 19, the microprocessor 20 determines the spatial location of the trackable device 10 as GPS latitude and longitudinal co-ordinates based on its location relative to the location of two of the fixed position transmitters 7 from which signals are being received by the second receiver 19. The microprocessor 20 is programmed to compute the spatial location of the trackable device 10 by triangulation based on the GPS latitude and longitude co-ordinates of the two fixed position transmitters 7 from which ZIGBEE signals are being received and from the strength of the received signals. The computed spatial location of the trackable device 10 in GPS latitude and longitude co-ordinates is then packaged into a transmittable data package which includes the unique identity code which identifies the specific trackable device 10 along with the GPS co-ordinates of the location of the trackable device 10. The packaged data is time and date stamped, and is then transmitted by the transmitter 21 in ZIGBEE format over standard internet protocol for reception by the tracking station 12.

In the event that the strength of the signal received by the second receiver 19 is stronger that the signal received by the first receiver 18, and a signal from only one of the fixed position transmitters 7 is being received by the second receiver 19, the microprocessor 20 continues to or reverts to determining the spatial location of the trackable device 10 from the satellite GPS system until signals from two of the fixed position transmitters 7 are being received. However, in the event that the first receiver 18 is unable to receive signals from the satellite GPS system, and a signal from only one of the fixed position transmitters 7 is being received by the second receiver 19, the microprocessor 20 attempts to determine the location of the trackable device 10 from the last known position of the trackable device 10, and from the signal received from the single fixed position transmitter 7. In the event of the microprocessor 20 being unable to determine the location of the trackable device 10 in this manner, the microprocessor 20 is programmed to produce a signal indicative of the zone of the compound 2 in which the trackable device 10 is most likely located. The signal indicative of the zone is then packaged into a suitable data signal along with the unique identity code of the trackable device 10, and the packaged data is time and date stamped, and is then transmitted by the transmitter 21 in ZIGBEE format over standard internet protocol for reception by the tracking station 12 at the next predefined millisecond time interval. A receiver 22 in the tracking station 12 receives the transmitted data packages from the trackable devices 10, which are read by a server 23. The server 23 in turn stores the locations and the corresponding times and dates of the respective trackable devices in a suitable memory (not shown) and displays the current locations of the respective trackable devices 10 on a visual display unit 24.

A battery 25 is provided within the housing 4 of each trackable device 10 for powering the first and second receivers 18 and 19, the microprocessor 20 and the transmitter 21 of the corresponding trackable device 10. The microprocessor 20 of each trackable device 10 is programmed to monitor the voltage level of the battery 25, and to include data indicative of the voltage level of the battery 25 in the respective data packages which contain the spatial location of the trackable device 10 and which are transmitted by the transmitter 21 at the predefined time intervals of 250 milliseconds. A temperature sensor 26 is located on an outer surface of the housing 4 of each trackable device 10 for monitoring the temperature of the child to which the trackable device 10 is attached. The microprocessor 20 of each trackable device 10 monitors signals from the corresponding temperature sensor 26 which are indicative of the temperature of the child to which the trackable device 10 is attached. The microprocessor 20 is programmed to include data indicative of the current temperature of the child in the respective data packages which include the spatial location of the trackable device 10 and which are transmitted by the transmitter 21 of the trackable device 10 at the predefined time intervals of 250 milliseconds. A detecting means comprising an electrical tamper switch 28 is located in the housing 14 of each trackable device 10 for detecting tampering with the trackable device 10, removal of the trackable device 10 from the child or loosening of the trackable device 10 on the child. A spring loaded plunger 29 which is spring urged outwardly of the housing 14 operates the tamper switch 28. The plunger 29 is located in the housing 14 and extends outwardly of the housing 14 to engage the wrist or arm of a child when the trackable device 10 is secured to the wrist or arm of the child 10 by the strap 15. While the housing 14 is tightly secured to the wrist or arm of a child by the strap 15, the plunger 29 is depressed inwardly into the housing 14 to thereby act on the tamper switch 28 to operate the tamper switch 28 in a closed circuit state. The plunger 29 is spring urged outwardly of the housing 14, and on the trackable device 10 being removed from the wrist or arm of the child or becoming loose on the wrist or arm of the child, or on an attempt to tamper with the trackable device, the plunger 29 is urged outwardly of the housing 14 under the spring urging to thereby operate the tamper switch 28 in an open circuit state. The microprocessor 20 is programmed to read signals from the tamper switch 28 in order to determine the status of the tamper switch 28. On determining that the tamper switch 28 is in the open circuit state, the microprocessor 20 is programmed to produce an alarm data signal which is indicative of the trackable device 10 having been removed from or loosened on the wrist or arm of the child or having been tampered with. The alarm data signal is packaged into a data package which includes a data signal indicative of the current spatial location of the trackable device 10, as well as other data which is normally transmitted by the transmitter 21 at the predefined time intervals of 250 milliseconds. The packaged data with the alarm signal is transmitted by the transmitter 21 for reception by the tracking station 12. The server 23 in the tracking station 12 is programmed so that on receipt of the alarm signal, a human sensory perceptible alarm signal is produced in the tracking station by activating both an audio alarm 31 and a visual alarm 32 to indicate that the trackable device 10 has been removed from or loosened on the wrist or arm of the child or has been tampered with.

The microprocessor 20 is also programmed to produce alarm data signals in the event of the spatial location of the trackable device 10 being indicative of the trackable device 10 being located outside the boundary 4 of the compound 2. The microprocessor 20 is also programmed to produce an alarm signal if the trackable device 10 remains in a predefined location for more than a predefined time, for example, if the trackable device 10 remained in a toilet or the like for more than a predefined time, of, for example, fifteen minutes. In each case the microprocessor 20 is programmed to produce the alarm data signal which is indicative of the trackable device 10 being located outside the boundary 4 of the compound 2 or the trackable device 10 having been in the predefined location for more than the predefined time, as the case may be. The microprocessor 20 is programmed to produce a data package which includes the appropriate alarm data signal, a data signal indicative of the spatial location of the trackable device together with the unique identity code of the trackable device 10. The data package is time and data stamped and is then transmitted by the transmitter 21 for reception by the tracking station 12. On receipt of either of these two data packages, the server 23 in the tracking station 12 is programmed to activate the audio and visual alarms 31 and 32 in the tracking station 12 to indicate that the trackable device 10 has either been located outside the boundary 4 of the compound 2 or has remained in a predefined location for more than the predefined time.

In this embodiment of the invention fixed position transmitters 7 are also located in the grounds of the compound 2 exteriorly of the buildings 5. Typically, such fixed position transmitters 7 are located in locations of the compound 2 where the satellite GPS signal may be relatively weak.

In use, each child the spatial location of which is to be monitored in the compound 2 is provided with one of the trackable devices 10, which is secured around the wrist of the child by the bracelet strap 15 and the clasp 16. As each child moves around the compound 2 and enters or exits buildings 5 within the compound and moves around within the buildings 5, the trackable device 10 of that child continuously at the predefined millisecond intervals determines and updates the spatial location of the trackable device 10, which is also the spatial location of the child. The current spatial location of the child is transmitted by the transmitter 21 of the trackable device 10, and is received by the receiver 22 of the tracking station 12 and relayed to the server 23 of the tracking station 12. The server 23 stores and displays the location of each child on the visual display unit 24, which can be observed by a person in the tracking station 12.

While the child is moving in the grounds of the compound 2 outside the buildings 5, the strength of the signal received by the first receiver 18 from the satellites of the satellite GPS system, in general, will be stronger than the signals received by the second receiver 19 from any of the fixed position transmitters 7. Thus, while the strength of the signal being received by the first receiver 18 from the satellites of the satellite GPS system is stronger than the signals being received by the second receiver 19, the microprocessor 20 continues to determine and update the spatial location of the trackable device 10 from signals received by the first receiver 18 from the satellites of the satellite GPS system. However, as the child commences to move from the grounds of the compound 2 into one of the buildings 5, while the strength of the signals received by the first receiver 18 from the satellites of the satellite GPS system are stronger than the signals received by the second receiver 19 from the fixed position transmitter 7, the microprocessor 20 continues to update the current location of the trackable device 10 from signals received by the first receiver 18 from the satellites of the satellite GPS system.

However, as soon as the strength of the signals received by the second receiver 19 from adjacent ones of the fixed position transmitters 7 becomes greater than the strength of the signal received by the first receiver 18 from the satellites of the satellite GPS system, the microprocessor 20 commences to determine the spatial location of the trackable device 10 from the signals received from one and preferably two of the adjacent fixed position transmitters 7 within the building 2. Similarly, as a child exits the building, the microprocessor 20 of the trackable device 0 continues to update the spatial location of the trackable device 10 from signals received from the fixed position transmitter 7 by the second receiver 19 until the strength of the signals received by the first receiver 18 from the satellites of the satellite GPS system exceeds the strength of the signals being received by the second receiver 19 from the fixed position transmitters 7. The temperature of each child is monitored in the tracking station, as is the voltage level of the battery 25 of each trackable device. In the event of a child displaying an abnormal temperature, the child is identified from the identity of the trackable device 10 which is attached to the child, and the child can be appropriately attended to. In the event of the voltage level of the battery 25 of any of the trackable device 10 falling below a predefined voltage level, the trackable device, the voltage level of the battery 25 of which is low can be replaced with another trackable device 10 on the child.

On the microprocessor 20 of any of the trackable devices 10 detecting removal from or loosening of the trackable device 10 on the wrist or arm of the child or tampering with the trackable device 10, the data package with the appropriate alarm signal is produced by the microprocessor 10 and transmitted by the transmitter 21 of the trackable device 10. On reception of the data package with the alarm signal by the tracking station 12, which activates the audio and visual alarms 31 and 32, appropriate action can be taken. Similarly, in the event of the microprocessor 20 of any of the trackable devices 10 detecting the location of the trackable device 10 being outside the boundary 4 of the compound 2, or a child remaining in a predefined location for greater than a predefined time period, the microprocessor 20 of that trackable device 10 produces the appropriate data package which includes the appropriate alarm signal. The data package with the appropriate alarm signal is then transmitted by the transmitter 21 of that trackable device 10, and on reception of the data package with the alarm signal, which activates the audio and visual alarm 31 and 32, appropriate action is taken by the tracking station 12.

While the trackable device has been described as being suitable for securing to the wrist of a child, the trackable device may be adapted for securing to any suitable part of a child, for example, the trackable device may be adapted for securing to the arm, ankle, leg or the like of a child, or may be provided as a pendant for wearing around the neck of a child. It is also envisaged that the trackable device may be secured around the body of a child, for example, around the waist by a belt or any other suitable attaching means. Needless to say, the trackable device may be adapted for attaching to an animal, if it were desired to track the spatial location of the animal as it moved around a compound.

Claims

1. A wireless trackable device comprising a first communicating means adapted for wirelessly communicating with a satellite global positioning system (GPS), a second communicating means adapted for wirelessly communicating with at least one land based wireless transmitter of known spatial location, a comparing means adapted for comparing the strength of signals received by the first and second communicating means with each other and for producing a select signal indicative of the one of the first and second communicating means, the strength of the received signals of which is strongest, a signal processing means adapted for determining the spatial location of the trackable device from signals read from the first and second communicating means, the signal processing means being responsive to the select signal from the comparing means for determining the spatial location of the trackable device from signals read from the one of the first and second communicating means, the strength of the received signals of which is strongest and for producing a signal indicative of the spatial location of the trackable device, and a transmitting means for wirelessly transmitting the signal indicative of the spatial location of the trackable device for reception by a tracking station.

2. A wireless trackable device as claimed in Claim 1 in which the first communicating means comprises a first wireless receiver.

3. A wireless trackable device as claimed in Claim 1 or 2 in which the first communicating means is adapted for receiving signals from at least one satellite of the satellite GPS system.

4. A wireless trackable device as claimed in any preceding claim in which the first communicating means is adapted for receiving signals from at least three satellites of the GPS system.

5. A wireless trackable device as claimed in any preceding claim in which the first communicating means is adapted for receiving signals from four satellites of the GPS system.

6. A wireless trackable device as claimed in any preceding claim in which the second communicating means comprises a second wireless receiver.

7. A wireless trackable device as claimed in any preceding claim in which the second communicating means is adapted for receiving signals from a plurality of the land based wireless transmitters of respective known spatial locations spaced apart from each other.

8. A wireless trackable device as claimed in any preceding claim in which the second communicating means is adapted for receiving signals from the respective land based wireless transmitters in ZIGBEE format.

9. A wireless trackable device as claimed in any preceding claim in which the signal processing means is adapted for determining the location of the trackable device as a function of latitude and longitude co-ordinates of the earth.

10. A wireless trackable device as claimed in any preceding claim in which the signal processing means is adapted for determining the location of the trackable device from the strength of signals received from at least one land based wireless transmitter.

11. A wireless trackable device as claimed in any preceding claim in which the signal processing means is adapted for determining the location of the trackable device from the strength of signals received from two land based wireless transmitters.

12. A wireless trackable device as claimed in any preceding claim in which the signal processing means comprises a first signal processing means for determining the location of the trackable device from signals received by the first communicating means from the at least one satellite of the satellite GPS system.

13. A wireless trackable device as claimed in Claim 12 in which the first signal processing means is adapted for determining the location of the trackable device from signals of at least three satellites of the satellite GPS system by a triangulation method.

14. A wireless trackable device as claimed in any preceding claim in which the signal processing means comprises a second signal processing means for determining the location of the trackable device from signals received from the at least one land based wireless transmitter.

15. A wireless trackable device as claimed in Claim 14 in which the second signal processing means is adapted for determining the location of the trackable device from signals received from at least two land based wireless transmitters by a triangulation method.

16. A wireless trackable device as claimed in any preceding claim in which the transmitting means is adapted for transmitting the signal indicative of the spatial location of the trackable device in ZIGBEE format.

17. A wireless trackable device as claimed in any preceding claim in which the trackable device comprises a housing.

18. A wireless trackable device as claimed in Claim 17 in which the housing comprises a waterproof housing.

19. A wireless trackable device as claimed in Claim 17 or 18 in which the first and second communicating means, the comparing means, the signal processing means and the transmitting means are located in the housing.

20. A wireless trackable device as claimed in any preceding claim in which a means for attaching the trackable device to an individual human or animal subject is provided.

21. A wireless trackable device as claimed in Claim 20 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching to a human subject.

22. A wireless trackable device as claimed in Claim 20 or 21 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to a wrist of a human subject.

23. A wireless trackable device as claimed in Claim 20 or 21 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to an ankle of a human subject.

24. A wireless trackable device as claimed in any of Claims 20 to 23 in which the means for attaching the trackable device to an individual human or animal subject comprises a strap.

25. A wireless trackable device as claimed in Claim 20 or 21 in which the means for attaching the trackable device to a human or animal subject comprises a lanyard extending from the trackable device and adapted so that the trackable device is wearable as a pendant.

26. A wireless trackable device as claimed in any of Claims 20 to 25 in which a detecting means is provided for detecting one of removal of the trackable device from a human or animal subject and loosening of the trackable device from the human or animal subject.

27. A wireless trackable device as claimed in Claim 26 in which the signal processing means is adapted to monitor the detecting means in order to detect the one of removal of the trackable device from the human or animal subject or the loosening of the trackable device from the human or animal subject.

28. A wireless trackable device as claimed in Claim 27 in which the signal processing means is responsive to a signal from the detecting means indicative of one of removal of the trackable device from the human or animal subject and loosening of the trackable device from the human or animal subject for producing an alarm signal and for operating the transmitting means to transmit the alarm signal indicative of removal or loosening of the trackable device from the human or animal subject.

29. A wireless trackable device as claimed in Claim 28 in which the alarm signal produced by the signal processing means indicative of removal or loosening of the trackable device from the human or animal subject comprises a data signal indicative of the spatial location of the trackable device.

30. A wireless trackable device as claimed in any preceding claim in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside a predefined area for producing an alarm signal.

31. A wireless trackable device as claimed in Claim 30 in which the alarm signal produced by the signal processing means in response to the determined spatial location of the trackable device being indicative of a location outside the predefined area comprises a data signal indicative of the spatial location of the trackable device,

32. A wireless trackable device as claimed in Claim 30 or 31 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside the predefined area for operating the transmitting means to transmit the alarm signal.

33. A wireless trackable device as claimed in any preceding claim in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in a predefined location for more than a predefined time period for producing an alarm signal.

34. A wireless trackable device as claimed in Claim 33 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in the predefined location for more than a predefined time period for operating the transmitting means to transmit the alarm signal.

35. A wireless trackable device as claimed in Claim 33 or 34 in which the alarm signal comprises a data signal indicative of the location of the trackable device.

36. A system for tracking a human or animal subject, the system comprising at least one land based wireless transmitter of known spatial location, a trackable device as claimed in any preceding claim adapted for attaching to the human or animal subject, and a tracking station for reading signals transmitted by the trackable device indicative of the spatial location of the trackable device.

37. A system as claimed in Claim 36 in which a plurality of land based wireless transmitters are provided spaced apart from each other, each land based wireless transmitter being of known spatial location.

38. A system as claimed in Claim 36 or 37 in which each land based wireless transmitter is adapted for transmitting a signal indicative of its spatial location.

39. A system as claimed in any of Claims 36 to 38 in which each land based wireless transmitter is adapted for transmitting a signal indicative of its GPS position.

40. A system as claimed in any of Claims 36 to 39 in which the signal transmitted by each land based wireless transmitter is indicative of the spatial location of the land based wireless transmitter produced as a function of the latitude and longitude co-ordinates of the spatial location of the land based wireless transmitter.

41. A system as claimed in any of Claims 36 to 40 in which each land based wireless transmitter is adapted for transmitting the signal indicative of the spatial location thereof in a ZIGBEE format.

42. A system for tracking a human or animal subject, the system comprising at least one land based wireless transmitter of known spatial location, a wireless trackable device adapted for attaching to the human or animal subject, the wireless trackable device comprising a first communicating means adapted for wirelessly communicating with a satellite global positioning system (GPS), a second communicating means adapted for wirelessly communicating with the at least one land based wireless transmitter of known spatial location, a comparing means adapted for comparing the strength of signals received by the first and second communicating means with each other and for producing a select signal indicative of the one of the first and second communicating means, the strength of the received signals of which is strongest, a signal processing means adapted for determining the spatial location of the trackable device from signals read from the first and second communicating means, the signal processing means being responsive to the select signal from the comparing means for determining the spatial location of the trackable device from signals read from the one of the first and second communicating means, the strength of the received signals of which is strongest and for producing a signal indicative of the spatial location of the trackable device, and a transmitting means for wirelessly transmitting the signal indicative of the spatial location of the trackable device, and a tracking station for remotely reading the signals transmitted by the trackable device which are indicative of the spatial location of the trackable device.

43. A system as claimed in Claim 42 in which a plurality of land based wireless transmitters are provided spaced apart from each other, each land based wireless transmitter being of known spatial location.

44. A system as claimed in Claim 42 or 43 in which each land based wireless transmitter is adapted for transmitting a signal indicative of its spatial location.

45. A system as claimed in any of Claims 42 to 44 in which each land based wireless transmitter is adapted for transmitting a signal indicative of its GPS position.

46. A system as claimed in any of Claims 42 to 45 in which the signal transmitted by each land based wireless transmitter is indicative of the spatial location of the land based wireless transmitter produced as a function of the latitude and longitude co-ordinates of the spatial location of the land based wireless transmitter.

47. A system as claimed in any of Claims 42 to 46 in which each land based wireless transmitter is adapted for transmitting the signal indicative of the spatial location thereof in a ZIGBEE format.

48. A system as claimed in any of Claims 42 to 47 in which the first

communicating means comprises a first wireless receiver.

49. A system as claimed in any of Claims 42 to 48 in which the first

communicating means is adapted for receiving signals from at least one satellite of the satellite GPS system.

50. A system as claimed in any of Claims 42 to 49 in which the first

communicating means is adapted for receiving signals from at least three satellites of the GPS system.

51. A system as claimed in any of Claims 42 to 49 in which the first

communicating means is adapted for receiving signals from four satellites of the GPS system.

52. A system as claimed in any of Claims 42 to 51 in which the second communicating means comprises a second wireless receiver.

53. A system as claimed in any of Claims 42 to 52 in which the second communicating means is adapted for receiving signals from a plurality of the land based wireless transmitters of respective known spatial locations spaced apart from each other.

54. A system as claimed in any of Claims 42 to 53 in which the second communicating means is adapted for receiving signals from the respective land based wireless transmitters in ZIGBEE format.

55. A system as claimed in any of Claims 42 to 54 in which the signal processing means is adapted for determining the location of the trackable device as a function of latitude and longitude co-ordinates of the earth.

56. A system as claimed in any of Claims 42 to 55 in which the signal processing means is adapted for determining the location of the trackable device from the strength of signals received from at least one land based wireless transmitter.

57. A system as claimed in any of Claims 42 to 56 in which the signal processing means is adapted for determining the location of the trackable device from the strength of signals received from two land based wireless transmitters.

58. A system as claimed in any of Claims 42 to 57 in which the signal processing means comprises a first signal processing means for determining the location of the trackable device from signals received by the first communicating means from the at least one satellite of the satellite GPS system.

59. A system as claimed in Claim 58 in which the first signal processing means is adapted for determining the location of the trackable device from signals of at least three satellites of the satellite GPS system by a triangulation method.

60. A system as claimed in any of Claims 42 to 59 in which the signal processing means comprises a second signal processing means for determining the location of the trackable device from signals received from the at least one land based wireless transmitter.

61. A system as claimed in Claim 60 in which the second signal processing means is adapted for determining the location of the trackable device from signals received from at least two land based wireless transmitters by a triangulation method.

62. A system as claimed in any of Claims 42 to 61 in which the transmitting means is adapted for transmitting the signal indicative of the spatial location of the trackable device in ZIGBEE format.

63. A system as claimed in any of Claims 42 to 62 in which the trackable device comprises a housing.

64. A system as claimed in Claim 63 in which the housing comprises a waterproof housing.

65. A system as claimed in Claim 64 in which the first and second

communicating means, the comparing means, the signal processing means and the transmitting means are located in the housing.

66. A system as claimed in any of Claims 42 to 65 in which a means for attaching the trackable device to an individual human or animal subject is provided.

67. A system as claimed in Claim 66 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching to a human subject.

68. A system as claimed in Claim 66 or 67 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to a wrist of a human subject.

69. A system as claimed in Claim 66 or 67 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to an ankle of a human subject.

70. A system as claimed in any of Claims 66 to 69 in which the means for attaching the trackable device to an individual human or animal subject comprises a strap.

71. A system as claimed in Claim 66 or 67 in which the means for attaching the trackable device to a human or animal subject comprises a lanyard extending from the trackable device and adapted so that the trackable device is wearable as a pendant.

72. A system as claimed in any of Claims 42 to 71 in which a detecting means is provided for detecting one of removal of the trackable device from a human or animal subject and loosening of the trackable device from the human or animal subject.

73. A system as claimed in Claim 72 in which the signal processing means is adapted to monitor the detecting means in order to detect the one of removal of the trackable device from the human or animal subject or the loosening of the trackable device from the human or animal subject.

74. A system as claimed in Claim 73 in which the signal processing means is responsive to a signal from the detecting means indicative of one of removal of the trackable device from the human or animal subject and loosening of the trackable device from the human or animal subject for producing an alarm signal and for operating the transmitting means to transmit the alarm signal indicative of removal or loosening of the trackable device from the human or animal subject.

75. A system as claimed in Claim 74 in which the alarm signal produced by the signal processing means indicative of removal or loosening of the trackable device from the human or animal subject comprises a data signal indicative of the spatial location of the trackable device.

76. A system as claimed in any of Claims 42 to 75 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside a predefined area for producing an alarm signal.

77. A system as claimed in Claim 76 in which the alarm signal produced by the signal processing means in response to the determined spatial location of the trackable device being indicative of a location outside the predefined area comprises a data signal indicative of the spatial location of the trackable device.

78. A system as claimed in Claim 76 or 77 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside the predefined area for operating the transmitting means to transmit the alarm signal.

79. A system as claimed in any of Claims 42 to 78 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in a predefined location for more than a predefined time period for producing an alarm signal.

80. A system as claimed in Claim 79 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in the predefined location for more than a predefined time period for operating the transmitting means to transmit the alarm signal.

81. A system as claimed in Claim 79 or 80 in which the alarm signal comprises a data signal indicative of the location of the trackable device.

82. A system as claimed in any of Claims 74 to 81 in which the tracking station comprises a means for producing a human sensory perceptible alarm signal, the means for producing the human sensory perceptible alarm signal being responsive to each one of the received alarm signals produced by the signal processing means of the trackable device for producing the human sensory perceptible alarm signal.

83. A system as claimed in Claim 82 in which the human sensory perceptible alarm signal produced by the means for producing the human sensory perceptible alarm signal is a visually perceptible signal.

84. A system as claimed in Claim 82 or 83 in which the human sensory perceptible alarm signal produced by the means for producing the human sensory perceptible alarm signal is an aurally perceptible signal.

85. A method for tracking a human or animal subject, the method comprising providing at least one land based wireless transmitter of known spatial location, attaching a wireless trackable device to the human or animal subject, the wireless trackable device being provided with a first wireless communicating means adapted for communicating with a satellite global positioning system, a second wireless communicating means adapted for communicating with the at least one land based wireless transmitter, a comparing means adapted for comparing the strength of signals received by the first and second communicating means with each other and for producing a select signal indicative of the one of the first and second

communicating means, the strength of the received signals of which is strongest, a signal processing means adapted for determining the spatial location of the trackable device from signals read from the first and second communicating means, the signal processing means being responsive to the select signal from the comparing means for determining the spatial location of the trackable device from signals read from the one of the first and second communicating means, the strength of the received signals of which is strongest and for producing a signal indicative of the spatial location of the trackable device, and a transmitting means for wirelessly transmitting the signal indicative of the spatial location of the trackable device, and remotely reading the signal from the trackable device which is indicative of the spatial location of the device to determine the location of the human or animal subject.

86. A method as claimed in Claim 85 in which a plurality of land based wireless transmitters are provided spaced apart from each other, each land based wireless transmitter being of known spatial location.

87. A method as claimed in Claim 85 or 86 in which each land based wireless transmitter transmits a signal indicative of its spatial location.

88. A method as claimed in any of Claims 85 to 87 in which each land based wireless transmitter transmits a signal indicative of its GPS position.

89. A method as claimed in any of Claims 85 to 88 in which the signal transmitted by each land based wireless transmitter is indicative of the spatial location of the land based wireless transmitter produced as a function of the latitude and longitude co-ordinates of the spatial location of the land based wireless transmitter.

90. A method as claimed in any of Claims 85 to 89 in which each land based wireless transmitter transmits the signal indicative of the spatial location thereof in a ZIGBEE format.

91. A method as claimed in any of Claims 85 to 90 in which the first

communicating means comprises a first wireless receiver.

92. A method as claimed in any of Claims 85 to 91 in which the first

communicating means receives signals from at least one satellite of the satellite GPS system.

93. A method as claimed in any of Claims 85 to 92 in which the first

communicating means receives signals from three satellites of the GPS system.

94. A method as claimed in any of Claims 85 to 93 in which the first

communicating means receives signals from four satellites of the GPS system.

95. A method as claimed in any of Claims 85 to 94 in which the second communicating means comprises a second wireless receiver.

96. A method as claimed in any of Claims 85 to 95 in which the second communicating means receives signals from a plurality of the land based wireless transmitters of respective known spatial locations spaced apart from each other.

97. A method as claimed in any of Claims 85 to 96 in which the second communicating means receives signals from the respective land based wireless transmitters in ZIGBEE format.

98. A method as claimed in any of Claims 85 to 97 in which the signal processing means determines the location of the trackable device as a function of latitude and longitude co-ordinates of the earth.

99. A method as claimed in any of Claims 85 to 98 in which the signal processing means determines the location of the trackable device from the strength of signals received from at least one land based wireless transmitter.

100. A method as claimed in any of Claims 85 to 99 in which the signal processing means determines the location of the trackable device from the strength of signals received from two land based wireless transmitters.

101. A method as claimed in any of Claims 85 to 100 in which the signal processing means determines the spatial location of the trackable device from signals received by the first communicating means from the at least one satellite of the satellite GPS system.

102. A method as claimed in Claim 101 in which the location of the trackable device is determined by a triangulation method.

103. A method as claimed in any of Claims 85 to 102 in which the signal processing means comprises a second signal processing means for determining the location of the trackable device from signals received from the at least one land based wireless transmitter.

104. A method as claimed in Claim 103 in which the location of the trackable device is determined by a triangulation method.

105. A method as claimed in any of Claims 85 to 104 in which the transmitting means is adapted for transmitting the signal indicative of the spatial location of the trackable device in ZIGBEE format.

106. A method as claimed in any of Claims 85 to 105 in which the trackable device comprises a housing.

107. A method as claimed in Claim 106 in which the first and second

108. A method as claimed in any of Claims 85 to 107 in which a means for attaching the trackable device to an individual human or animal subject is provided.

109. A method as claimed in Claim 108 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching to a human subject.

110. A method as claimed in Claim 108 or 109 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to a wrist of a human subject.

111. A method as claimed in Claim 108 or 109 in which the means for attaching the trackable device to an individual human or animal subject is adapted for attaching the trackable device to an ankle of a human subject.

112. A method as claimed in any of Claims 108 to 111 in which the means for attaching the trackable device to an individual human or animal subject comprises a strap.

113. A method as claimed in Claim 108 or 109 in which the means for attaching the trackable device to a human or animal subject comprises a lanyard extending from the trackable device so that the trackable device is wearable as a pendant.

114. A method as claimed in any of Claims 108 to 113 in which a detecting means is provided for detecting one of removal of the trackable device from a human or animal subject and loosening of the trackable device from the human or animal subject.

115. A method as claimed in Claim 114 in which the signal processing means monitors the detecting means in order to detect the one of removal of the trackable device from the human or animal subject or the loosening of the trackable device from the human or animal subject.

116. A method as claimed in Claim 115 in which the signal processing means is responsive to a signal from the detecting means indicative of one of removal of the trackable device from the human or animal subject and loosening of the trackable device from the human or animal subject for producing an alarm signal and for operating the transmitting means to transmit the alarm signal indicative of removal or loosening of the trackable device from the human or animal subject.

117. A method as claimed in Claim 116 in which the alarm signal produced by the signal processing means indicative of removal or loosening of the trackable device from the human or animal subject comprises a data signal indicative of the spatial location of the trackable device.

118. A method as claimed in any of Claims 85 to 117 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside a predefined area for producing an alarm signal.

119. A method as claimed in Claim 118 in which the alarm signal produced by the signal processing means in response to the determined spatial location of the trackable device being indicative of a location outside the predefined area comprises a data signal indicative of the spatial location of the trackable device.

120. A method as claimed in Claim 118 or 119 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of a location outside the predefined area for operating the transmitting means to transmit the alarm signal.

121. A method as claimed in any of Claims 85 to 120 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in a predefined location for more than a predefined time period for producing an alarm signal.

122. A method as claimed in Claim 121 in which the signal processing means is responsive to the determined spatial location of the trackable device being indicative of the trackable device being in the predefined location for more than a predefined time period for operating the transmitting means to transmit the alarm signal.

123. A wireless trackable device as claimed in Claim 33 or 34 in which the alarm signal comprises a data signal indicative of the location of the trackable device.

124. A method as claimed in any of Claims 85 to 123 in which a tracking station is provided for remotely reading the signals transmitted by the trackable device which are indicative of the spatial location of the trackable device.

125. A method as claimed in Claim 124 in which the tracking station receives the signals indicative of the spatial location of the trackable device in a ZIGBEE format.

126. A method as claimed in Claim 124 or 125 in which the tracking station comprises a means for producing a human sensory perceptible alarm signal, the means for producing the human sensory perceptible alarm signal being responsive to each one of the received alarm signals produced by the signal processing means of the trackable device for producing the human sensory perceptible alarm signal.

127. A method as claimed in Claim 126 in which the human sensory perceptible alarm signal produced by the means for producing the human sensory perceptible alarm signal is a visually perceptible signal.

128. A method as claimed in Claim 126 or 127 in which the human sensory perceptible alarm signal produced by the means for producing the human sensory perceptible alarm signal is an aurally perceptible signal.