EP1044439B1

EP1044439B1 - Person locating system

Info

Publication number: EP1044439B1
Application number: EP98960671A
Authority: EP
Inventors: Michael D. Westrick; Peter F. Johnson; Scott A. Brune
Original assignee: Innotek Pet Products Inc
Current assignee: Innotek Pet Products Inc
Priority date: 1997-12-04
Filing date: 1998-12-03
Publication date: 2003-03-12
Anticipated expiration: 2018-12-03
Also published as: EP1044439A1; PT1044439E; DE69812178T2; DK1044439T3; WO1999028881A1; ATE234492T1; DE69812178D1; ES2189280T3

Abstract

A person locating system (10) for detecting the unauthorized exit of a person from a monitored area (18) and locating the person thereafter, including a boundary transmitter (52) which generates an activation signal that is conducted across a conductor (16) connected to the boundary transmitter (36). The conductor (16) extends along a boundary of the monitored area (18) and transmits the activation signal within an activation zone (15) adjacent the conductor (16). The person to be monitored wears a portable module (22), which remains in a low power consumption, standby mode until the person enters the activation zone (15) adjacent the conductor (16). The portable module (22) receives the activation signal and enters an active mode wherein the portable module (22) transmits a high frequency locator signal (for example, 220 MHz). The locator signal is received by a locator receiver (28), which may be installed in a facility within the monitored area (18). The locator receiver (28) may also be portable so that the person to be monitored can be tracked down and recovered. In an alternate embodiment, the portable modules (22) are encoded with unique identification information which is transmitted as a part of the locator signal. The locator receiver (56) decodes this information and displays the identification of the wearer of the portable module (22) on a display (64).

Description

Background and Summary of the Invention

The present invention as it is defined in the appended claims relates to a system for detecting the unauthorized exit of a person from a monitored area and tracking the position of the person thereafter.
It is desirable for hospitals, nursing homes, adult day care centers. and rehabilitation centers to provide outdoor access to residents to facilitate exercise and recreation. It is also desirable to provide a monitored area without walls, fences. or other physical barriers to egress from the monitored area, such as disclosed in U.S. Patent No. 4,733,633. However, residents of such facilities sometimes wander outside of the monitored area because of confusion or disorientation caused by Alzheimer's disease, Down's Syndrome, traumatic brain injury, or autism. Accordingly, there exists a need for a system for monitoring the movement of such residents, particularly, their unauthorized exit from designated areas within or surrounding such facilities. One such monitoring system is disclosed in the publication entitled "Technology development in the RF tracking and locating of personnel and objects" (pp. 206-212) by Gary Loubert, presented at the Proceedings of the International Camahan Conference on Security Technology: Crime Countermeasures, Atlanta, October 14-16, 1992. Moreover, because of the obvious dangers associated with the random wandering of confused residents, and the difficulties in locating them after their unauthorized exit. there exists a need for a system which immediately indicates an unauthorized exit, and permits tracking, location and recovery of the wandering resident. It is further desirable to provide a system which requires minimum maintenance and servicing.
Accordingly, the present invention provides a locating system as defined by independent claims 1, 22 and 32 and a locating method as defined by independent claim 34.
In one embodiment, therefore, the present invention provides a person locating system which is actuated when the person leaving the monitored area breaches a perimeter zone. Each person within the monitored area wears a portable module which operates at very low power when in standby mode. A boundary transmitter generates an activation signal and transmits it across a conductor which establishes the perimeter of the monitored area. The conductor transmits the activation signal within an activation zone immediately adjacent the conductor. When the wandering resident enters the activation zone, a receiver within the portable module receives the activation signal and switches the module into active mode. A transmitter within the portable module then transmits a locator signal. A locator receiver mounted within the facility receives the locator signal and activates an alarm indicating an unauthorized exit. Facility personnel then use a hand held portable locator to determine the location of the wandering resident. The portable module remains in the active mode until manually deactivated to return to the standby mode. Once located, the portable module can be placed in the standby mode by operation of a magnetic switch further comprised therein.
Other objects, advantages and novel features of the present invention will be apparent upon consideration of the following description of the preferred embodiments and accompanying drawings.

Brief Description of the Drawings

Fig. 1 is a conceptual diagram of the person locating system of the present invention as employed in a facility.
Fig. 2 is a schematic block diagram of a portable module according to the present invention.
Fig. 3 is a schematic block diagram of a boundary unit according to the present invention.
Fig. 4 is a perspective view of a portable locator receiver according to the present invention.
Fig. 5 is a schematic block diagram of the portable locator receiver shown in Fig. 4.
Fig. 6 is a schematic block diagram of an alternate embodiment of a portable locator receiver according to the present invention.

Detailed Description of the Embodiments of the Invention

The embodiments described herein are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Rather, the embodiments selected for description are disclosed so that others skilled in the art may utilize their teachings.
Although the following description presents the system according to the present invention as a system for locating people, specifically, residents of particular facilities, it should be understood that the invention could readily be adapted, for example, to monitor and locate children, prisoners, animals, vehicles, and other movable objects which are to be kept within a specific area.
Fig. I depicts a person locating system according to the present invention generally designated by the numeral 10. System 10 generally includes a boundary unit 12 which is plugged into a standard AC outlet within the residential facility 20. Boundary unit 12 is electrically connected through wires 14 to a wire loop. 16 surrounding a monitored area 18 outside facility 20. In an exemplary embodiment, the wire loop 16 is 18 gauge wire which is buried one to three inches (about 2.5 cm. to about 7.6 cm.) in the ground around the perimeter of a monitored area 18 up to 25 acres in size.
System 10 further includes a portable module 22 to be worn by the residents around a limb, such as on the ankle or wrist. Portable module 22 includes a strap 24 for attachment around the resident's limb, and a control unit 26 which includes a receiver and transmitter as is described in greater detail below.
In general, when boundary unit 12 is activated, it generates an activation signal which it transmits across wires 14 and through wire loop 16. Wire loop 16 emits the activation signal through the ground and the air adjacent the wire loop, thereby defining an activation zone 15 around the wire loop. A resident wearing a portable module 22 may move freely within facility 20 or outside of facility 20 within monitored area 18. So long as the resident remains within the monitored area 18, the portable module remains inactive, in a low power, standby mode. When the resident crosses wire loop 16, or otherwise enters activation zone 15, control unit 26 of portable module 22 receives the activation signal emanated by wire loop 16 and switches to an active mode. When in active mode, control unit 26 transmits a high frequency locator signal (for example, 220 megahertz) which is received by a receiver in boundary unit 12. Boundary unit 12 then activates an alarm. Additional receivers 28 may be located throughout facility 20 to receive the locator signal transmitted by control unit 26. As described in greater detail below, facility personnel then may use a hand held locator 30 (Fig. 4) to locate the resident.
Fig. 2 is a schematic block diagram of the control unit 26 of portable module 22. Control unit 26 includes a microcontroller 32, such as an MC68HC705J1A, a receiver section 34 and a transmitter section 36. Control unit 26 is powered by a battery 37 which, in an exemplary embodiment, consists of a pair of three volt coin cell lithium batteries having a combined output current of 220 milliamps. Control unit 26 is turned on and off by actuation of magnetic reed switch 38. Microcontroller 32 is connected to oscillator 39.
Receiver section 34 includes an antenna 40 for receiving the activation signal emitted by wire loop 16. Antenna 40 is a 10 kilohertz ferrite antenna. Antenna 40 is connected to amplification stage 42 which amplifies the signal received by antenna 40 for output to microcontroller 32. Transmitter section 36 includes an oscillator 44 which provides a 10.245 megahertz reference signal to the remainder of the transmitter section 36. Oscillator 44 is connected to a signal processing section 46 which provides the function of a commonly known phase lock loop synthesizer. The output signal of the signal processing section 46 is filtered and amplified by the harmonic filter/amplification stage 48. Filter/amplification stage 48 is routed to antenna 50, which is a 220 megahertz, low profile, load insensitive, ferrite antenna.
Because control unit 26 is normally in a standby mode (i.e., in a receiving mode waiting to detect an activation signal), the battery life is on the order of months. When a 10 kilohertz activation signal is detected, microcontroller 32 switches control unit 26 into an active mode, wherein transmitter section 36 generates the 220 megahertz locator signal. Control unit 26 consumes substantially more power when in active mode. Accordingly, the active battery life is on the order of two days.
Fig. 3 depicts boundary unit 12, which generally includes a boundary transmitter 52, a microcontroller 54 such as an MC68HC705J1A, and a locator receiver 56. Boundary unit 12 further includes a power supply 58 which is plugged into a 110 volt alternating current supply line within the facility 20. Power supply 58 is connected to a voltage regulator 60 and amplifier 62 of boundary transmitter section 52. Voltage regulator 60 is connected to microcontroller 54 and display 64 (used in an alternate embodiment of the present invention as described below). A four megahertz oscillator 66 provides an input to microcontroller 54. Microcontroller 54 is also connected to an audible alarm 68, which indicates the occurrence of a perimeter breach. As shown in Fig. 3, the amplified 10 kilohertz activation signal from boundary transmitter section 52 is transmitted across wires 14 around wire loop 16.
Locator receiver 56 is connected to antenna 70, which is an omni directional 220 megahertz whip antenna. Antenna 70 is connected to amplifier 72 which provides an input to summing junction 74. The other input is provided by signal processor section 76 which is connected to microcontroller 54 and 10.245 megahertz oscillator 78, and provides a phase lock loop synthesizer function. The output of summing junction 74 is connected to harmonic filter/amplification stage 80 which includes a 10.7 megahertz filter having a 15 kilohertz bandwidth. The output of filter/amplification stage 80 is connected to summing junction 82, which also receives an oscillation signal from oscillator 78. The output of summing junction 82 is connected to harmonic filter/amplification stage 84, which includes a 455 kilohertz filter having a 15 kilohertz bandwidth. Harmonic filter/amplification stage 84 is connected to summing junction 86, which also receives an input from 455 kilohertz oscillator 88. Summing junction 86 is connected to harmonic filter/amplification stage 90, which includes a 10 kilohertz audio filter. Filter/amplification stage 90 is connected to signal detector 91, which provides an interrupt to microcontroller 54 when a locator signal is present. As shown, the output of the locator receiver section is fed back to microcontroller 54.
Fig. 5 is a schematic block diagram of a portable locator receiver or hand held locator 30 according to the present invention. Portable locator receiver 30 includes a microcontroller 92 (e.g., MC68HC705J1A) and a receiver section which substantially corresponds to locator receiver section 56 of boundary unit 12 (Fig. 3). Locator 30 includes antenna 94 which is a directional, three element antenna for receiving signals within the range of 216-220 megahertz. As best shown in Fig. 4, antenna 94 includes a main body 148, and three pairs of collapsible perpendicular branches 150. Housing 152 encloses substantially all of the electronics shown in Fig. 5.
The signal from antenna 94 is amplified by amplifier 96 and routed to harmonic filter/amplification stage 98, which includes a 216-220 megahertz filter. Stage 98 is connected to summing junction 100 which also receives an input from signal processing section 102. Signal processing section 102 is likewise substantially the same as signal processing section 76 of boundary unit 12. A voltage controlled oscillator 104 provides an input to signal processing section 102 and summing junction 108 Oscillator 104 is connected to frequency control potentiometer 106 which permits fine adjustment of the oscillator output signal within a five kilohertz range from 10.2445 megahertz to 10.2455 megahertz. The output of summing junction 100 is connected to harmonic filter/amplification stage 110 which includes a 107 megahertz filter having a 15 kilohertz bandwidth. The output of summing junction 108 is connected to harmonic filter/amplification stage 112 which includes a 455 kilohertz filter having a 15 kilohertz bandwidth. Summing junction 114 combines the output of filter/amplification stage 112 and the signal from 455 kilohertz oscillator 116. Oscillator 116 also provides a 455 kilohertz reference signal to microcontroller 92. Summing junction 114 is connected to amplifier 118 which, in turn, is connected to harmonic filter/amplification stage 120. Stage 120 includes a 300 hertz base band filter. An additional 300 hertz base band filter is included in filter/amplification stage 122, which also receives a one kilohertz on/off channel tone from microcontroller 92. The output of the receiver section is provided to an external head phone jack 124, a signal detector 126 and a one kilohertz piezo speaker 128. Detector 126 is connected to signal strength meter 130 which is operably associated with back light LED 132. The output of 220 megahertz receiver is fed back to microcontroller 92. External jack 124, speaker 128, meter 130, and frequency control potentiometer 106 are appropriately mounted to housing 152.
Locator 30 is powered by a nine volt alkaline battery 134 which is fed through a voltage regular 136 to provide the appropriate voltage level for the locator electronics. The amplification stages included in the receiver section of locator 30 have adjustable gains. The gain of these amplifiers is controlled by the voltage output of adjustable voltage regulator 138. By manually adjusting signal attenuator 140 (also mounted to housing 152), output V (GAIN) is varied by adjustable voltage regulator 138. Consequently, the operator can adjust the gain of the receiver relative to the signal strength of the locator signal received by antenna 94. Finally, an on/off switch 142 and a back light control switch 144 are connected to microcontroller 92. Both switches are mounted on housing 152.
In operation, power supply 58 of boundary unit 12 is plugged into a 110 volt outlet within facility 20. Boundary unit 12 then generates and transmits a 10 kilohertz pulse code modulated signal across wires 14 and wire loop 16. This continually-transmitted activation signal is sufficiently powerful to emanate from loop 16 to define activation zone 15 adjacent loop 16.
Before residents of facility 20 are permitted to move unsupervised within monitored area 18, the residents are fitted with a portable module 22. Portable module 22 is strapped or otherwise attached around a limb of the resident, preferably the resident's ankle. Switch 38 is actuated, thereby turning on control unit 26. Control unit 26 remains in standby mode (i.e., receiver mode wherein control unit 26 dissipates very low power) until the resident enters the activation zone 15 adjacent perimeter wire loop 16. Once the resident is sufficiently close to wire loop 16, receiver section 34 of control unit 26 detects the 10 kilohertz activation signal. Antenna 40 receives the activation signal, which is then amplified by amplification stage 42.
Microcontroller 32 responds by activating the transmitter section 36 of control unit 26 (i.e., switches into active mode). Once activated, transmitter section 36 generates a 220 megahertz locator signal, which it transmits from antenna 50. The locator signal is generated based on the 10.245 megahertz reference oscillator 44, which is processed by signal processing section 46 and filtered and amplified by harmonic filter/amplification stage 48. Once activated, the transmitter section 36 of control unit 26 transmits the 220 megahertz locator signal until battery 38 drains or switch 38 is switched off. The locator signal indicates the unauthorized exit of a resident from monitored area 18 and provides a beacon signal to facilitate the location and recovery of the wandering resident.
The 220 megahertz locator signal is received by antenna 70, which is connected to locator receiver 56 as best shown in Fig. 3. The signal received by antenna 70 is amplified at amplifier 72 and then combined with the output of signal processing section 76 in a manner commonly known in the art. The output of summing junction 74 is passed through the 10.7 megahertz harmonic filter of filter/amplification stage 80. The resulting signal is amplified and combined with the 10.245 megahertz reference oscillator signal from oscillator 78. The output of summing junction 82 is again passed through a filter and amplified by filter/amplification stage 84. The amplified output of the 455 kilohertz band-pass filter included in filter/amplification stage 84 is combined with the 455 kilohertz output of oscillator 88 at summing junction 86. The output of summing junction 86 is passed through a 10 kilohertz audio filter and amplified in filter/amplification stage 90
Finally, the output of amplifier 90 is passed through detector 91, which provides microcontroller 54 with an interrupt signal indicating the detection of a locator signal. Microcontroller 54 responds by activating audible alarm 68 to notify facility personnel that a resident has left the monitored area 18 without authorization. The facility personnel may then attempt to immediately recover the wandering resident.
Alternatively, facility personnel may use hand held locator 30 to pinpoint the location of the resident who has breached the perimeter of the monitored area 18. By pointing locator 30 in various directions, the operator can determine the position of the resident wearing a portable module 22 in active mode. Directional antenna 94 receives the 220 megahertz locator signal from portable module 22 at a higher intensity when antenna 94 is directed toward portable module 22. If the wandering resident has traveled a relatively great distance from the facility 20, the operator can adjust signal attenuator 140 to its maximum position, thereby causing adjustable voltage regulator 138 to output a voltage level corresponding to maximum gain in the amplification stages of locator 30. When V (GAIN) is at its maximum level, antenna 94 is most sensitive and can receive even relatively weak locator signals. The signal received by antenna 94 is amplified at amplification stage 96 and then passed through a 216-220 megahertz filter at harmonic filter/amplification stage 98. The filtered output of stage 98 is then summed with the output of signal processing section 102 and passed through a 10.7 megahertz band-pass filter included in the filter/amplification stage 110. The output of stage 110 is combined with the output of voltage controlled oscillator 104.
The output frequency of voltage controlled oscillator 104 can be adjusted by adjusting frequency control potentiometer 106. The range of adjustment, in an exemplary embodiment, is plus or minus five kilohertz. This adjustment permits fine tuning of the receiver to compensate for frequency drift of the transmitter section of control unit 26 and the internal oscillators of locator receiver 30.
The output of summing junction 108 is then passed through a 455 kilohertz band-pass filter and amplified at filter/amplification stage 112. This filtered signal is combined with the output of the 455 kilohertz reference oscillator 116 at summing junction 114. The resultant signal is amplified at amplifier 118 and passed through a pair of 300 hertz base band filter/amplification stages 120, 122. The final output of the receiver portion of locator 30 excites speaker 128 which emits an audible one kilohertz beat tone. After the signal is passed through detector 126, it is provided as an input to meter 130 Meter 130 provides a visual indication of the signal strength by varying the position of a needle on the face of the meter. As is commonly employed in this and related fields of art, the visual feedback provided by the meter assists the operator in aiming the hand held locator to further pinpoint the position of the wandering resident. When locator 30 is pointed directly at the resident, the position of the needle on meter 130 will correspond to maximum signal strength.
Locator 30 can be operated at night or under low light conditions by switching on switch 144, thereby causing microcontroller 92 to excite the back light LED 132 which emits light to illuminate the face of meter 130. Additionally, the operator can receive audible feedback on the position of the wandering resident by using headphones which are plugged into the external headphone jack connected to the output of filter/amplification stage 122, as shown in Fig. 5.
As the operator of the hand held locator 30 becomes nearer and nearer to the wandering resident, the strength of the locator signal transmitted by portable module 22 increases. The operator can decrease the gain of the receiver amplifier stages using signal attenuator 140 to maintain the received signal within the operating range of the receiver. Eventually, the operator will establish visual contact with the wandering resident. Once the resident is recovered, portable module 22 may be placed back into standby mode by switching magnetic switch 38.
In an alternate embodiment of the present invention, microcontroller 32 of control unit 26 is programmed through receiver 34 to transmit a particular pulse width encoded signal as a locator signal, which is unique to the particular portable unit 22. Accordingly, the 220 megahertz locator signal, which portable module 22 transmits once actuated by a 10 kilohertz activation signal, is encoded with this unique identification information. In a preferred embodiment of the present invention, 400 frequency channels may be employed, each using one of 32 modulation codes (resulting in a possible 12,800 unique I.D.s).
The boundary unit 12 of this alternate embodiment includes a microcontroller 54 which is programmed to decode the encoded activation signals. The locator receiver 56 scans each frequency channel to detect a valid activation signal. Once a signal is detected, it is decoded to determine the unique electronic I.D. associated with the portable module 22 worn by the resident who breached the perimeter of the monitored area 18.
The boundary unit 12 of this alternate embodiment employs I.D. code display 64 which is a 20 character, two line, liquid crystal display manufactured by Toshiba. Microcontroller 54 provides an output signal corresponding to the I.D. of the particular portable module 22 currently being detected. This signal is received by display 64 which provides a visual identification (either a number or name) associated with the resident assigned to the presently activated portable module 22.
Likewise, hand held locator 30 may readily be adapted to incorporate a display, as shown in Fig. 6. Display 160 is mounted to housing 152 and receives as its input the output of filter/amplification stage 122. Display 160 is plugged into external headphone jack 124. The audible pulses emitted by the transmitter section of control unit 26 are pulse width encoded, as described above, and decoded by microcontroller 92 which has been programmed to recognize the specific I.D. codes associated with each of the portable modules 22. Microcontroller 92 decodes the signal and provides an output to display 160 which the display interprets to provide a positive identification of the detected portable module 22.
While this invention has been described as having exemplary embodiments, this application is intended to cover any variations, uses, or adaptations using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice within the art to which it pertains. The scope of the invention are to be limited only by the terms of the appended claims.

Claims

A locating system (10), comprising:

a boundary unit (12) which generates an activation signal;

a conductor (16) connected to the boundary unit, the conductor extending along a boundary of a monitored area (18) and transmitting the activation signal within an activation zone (15) adjacent the conductor;

a portable module (22) including a receiver (34) for receiving the activation signal when the portable module (22) enters the activation zone (15), the receiver switching the portable module (22) from a standby mode to an active mode upon receipt of the activation signal and a transmitter (36) which transmits a locator signal when the portable module (22) is in the active mode;

characterized in that:

the portable module is operable to remain in the active mode until manually deactivated to return to the standby mode; and

the portable module further comprises a magnetic switch (38) for placing the portable module into the standby mode.
A locating system (10) according to claim 1 wherein the boundary unit (12) is connected to a 110 volt alternating current power source.
A locating system (10) according to claim 1 wherein the boundary unit (12) is connected to a battery.
A locating system (10) according to claim 1 wherein the conductor (16) is a wire submerged below the surface of the monitored area (18) and extending along the perimeter of the monitored area (18).
A locating system (10) according to claim 1 wherein the conductor (16) is a wire disposed above the surface of the monitored area (18) and extending along the perimeter of the monitored area (18).
A locating system (10) according to claim 1 wherein the conductor (16) continuously transmits the activation signal as a pulse code modulated signal at a frequency below approximately 20 kilohertz.
A locating system (10) according to claim 1 wherein the portable module (22) includes an adjustable strap (24) for attachment to a wearer.
A locating system (10) according to claim 1 wherein the portable module (22) includes an ankle bracelet (24).
A locating system (10) according to claim 1 wherein the portable module (22) includes a waterproof housing which encloses the portable module receiver (34) and transmitter (36).
A locating system (10) according to claim 1 wherein the portable module transmitter (36) transmits the locator signal at a frequency in the range of approximately 216 to 221 megahertz.
A locating system (10) according to claim 1 wherein the locator signal includes pulse coded information for distinguishing the portable module (22) from other portable modules.
A locating system (10) according to claim 1 further comprising a locator receiver (30,56) for receiving the locator signal, thereby permitting the location of the portable module (22).
A locating system (10) according to claim 12 wherein the locator receiver (56) is mounted within the monitored area (18).
A locating system (10) according to claim 12 wherein the locator receiver (56) includes an alarm (68) which is activated upon receipt of the locator signal.
A locating system (10) according to claim 12 wherein the locator receiver (30) is portable.
A locating system (10) according to claim 12 wherein the locator receiver (30, 56) is a super-heterodyne direction-finding receiver.
A locating system (10) according to claim 12 wherein the locator receiver (30) includes an adjustable attenuator (140) for varying the gain of the receiver.
A locating system (10) according to claim 12 wherein the locator receiver (30) includes a meter (130) to indicate the strength of the locator signal.
A locating system (10) according to claim 12 wherein the locator receiver (30) includes a tuner (106) for adjusting the reception frequency of the locator receiver (30).
A locating system (10) according to claim 11 further comprising a locator receiver (30) having a display (160) for displaying the locator signal information distinguishing the portable module (22) from other portable modules.
A locating system (10) according to claim 20 wherein the display (160) is a liquid crystal display.
A locating system (10), comprising:

a boundary unit (12) connected to a conductor (16) which extends along a boundary of a monitored area (18), the boundary unit (12) continuously transmitting an activation signal through the conductor (16) which emanates into an activation zone (15) adjacent the conductor (16); and

a portable module (22) including a receiver (34) and a transmitter (36), the receiver (34) receiving the activation signal upon entering the activation zone (15), the portable module (22) responding to the activation signal by switching from a standby mode into an active mode, wherein the portable module transmitter (36) transmits a locator signal to the boundary unit (12) while in the active mode;

characterized in that:

the portable module is operable to remain in the active mode until manually deactivated to return to the standby mode; and

the portable module further comprises a magnetic switch (38) for placing the portable module into the standby mode.
A locating system (10) according to claim 22 wherein the conductor (16) is a buried wire extending along the perimeter of the monitored area (18).
A locating system (10) according to claim 22 wherein the portable module (22) is adapted to be worn by a person.
A locating system (10) according to claim 22 wherein the portable module (22) is in the form of an ankle bracelet (24).
A locating system (10) according to claim 22 wherein the portable module (22) is programmable to transmit a locator signal including information identifying the portable module (22).
A locating system (10) according to claim 22 further comprising a portable locator receiver (30) for receiving the locator signal.
A locating system (10) according to claim 27 wherein the portable locator receiver (30) is a super-heterodyne direction-finding receiver.
A locating system (10) according to claim 27 wherein the portable locator receiver (30) includes a gain adjustment (140).
A locating system (10) according to claim 27 wherein the portable locator receiver (30) includes a frequency tuner (106).
A locating system (10) according to claim 26 wherein the boundary unit (12) includes a display (64) for displaying the identifying information.
A locating system (10), comprising:

means (12) for generating an activation signal;

means (16) operably associated with the generating means for conducting the activation signal along a boundary of an area being monitored, the conducting means transmitting the activation signal within an activation zone (15);

means (22) attachable to a movable object to be monitored for receiving the activation signal upon entry into the activation zone (15), the activation signal receiving means (22) including means (32, 34) for switching from a standby mode into an active mode upon receipt of the activation signal and means (36) for continuously transmitting a locator signal in response to the activation signal; and

means (30, 56) for receiving the locator signal;

characterized in that:

the means attachable to a movable object is operable to remain in the active mode until manually deactivated to return to the standby mode; and

the means attachable to a movable object further comprises a magnetic switch (38) for placing said means into the standby mode.
A locating system (10) according to claim 32 wherein the locator signal receiving means (30) is hand-held.
A method of locating a movable object to be monitored, comprising:

attaching a portable module (22) to said object;

generating an activation signal;

conducting the activation signal along a boundary of an area being monitored and transmitting the activation signal within an activation zone (15);

receiving the activation signal by means of said portable module upon entry of said portable module into the activation zone (15);

receipt of the activation signal switching the portable module from a standby mode into an active mode and causing it to continuously transmit a locator signal in response to the activation signal; and

receiving the locator signal;

characterized by:

maintaining the portable module in the active mode until manually deactivated to return to the standby mode; and

placing the portable module into the standby mode by means of a magnetic switch (38) comprised therein.