Abstract:
A wireless valuables monitoring device, with proximity sensing and automatic arming and disarming features two way communication between the base unit affixed to the valuable and the remote unit carried by the owner. The base unit continuously monitors the position of the remote unit relative to itself to determine when the owner has left the immediate vicinity of the valuable. The base unit alerts the owner upon disturbance of the protected valuable and allows the user to screen for false alarms and be notified of an occurring theft attempt. A soft power switch enables the base unit to be powered off by the unique remote unit to which it belongs.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from U.S. application No. 60/441,920 filed on 24 Jan. 2003, which is hereby incorporated by reference herein. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The invention relates to apparatus and methods for detecting when an object is disturbed and generating an alarm in response thereto. The invention has general application to protecting valuables. Some embodiments of the invention are applied to protect laptop computers or other portable electronic devices.  
         BACKGROUND  
         [0003]    The theft or loss of valuable belongings is a problem, especially for those who need to leave or use such valuable belongings in public areas. Valuables may be stolen or tampered with if left unattended even for short periods. A person&#39;s valuables can be exposed to risk by common events such as when the person goes to the washroom, takes time away from the office for lunch or coffee, travels by car, bus, train or airplane, or checks into a hotel. Items from purses, briefcases, luggage, wallets, cellular phones, Personal Digital Assistants (PDAs), digital cameras, music players, Liquid Crystal Displays (LCDs), LCD projectors, and laptop computers are just some of the small, but valuable, items that thieves are targeting today.  
           [0004]    The theft of a laptop computer can be particularly costly because laptop computers often store information that is confidential and/or very difficult to recreate. More and more laptop computers are used each year as mobile computing replaces conventional desktop computers. Over 100 million laptops are in use worldwide and laptop sales have been continuously increasing. In 2002 alone, notebook computer sales increased by 11% while more portable computers such as PC tablets were introduced to the market. Correspondingly, theft of laptop computers has also been increasing year by year. Last year, more than 640,000 laptops were stolen, resulting in a $60 billion loss in both hardware and stored software and data. Roughly 65% percent of the total thefts occurred on the road and in airports while 29% took place at the office.  
           [0005]    Guarding against the theft of portable valuables, and particularly portable computers and other electronic devices is a major issue that has yet to be appropriately addressed. Current anti-theft solutions and theft deterrent systems range from passive devices, such as tethers which can be used to lock a computer to a desk or table, to more complex separation detectors, 2-way signaling devices, and motion alarms.  
           [0006]    Motion alarms can be triggered by an authorized user of the device if the user forgets to disarm the motion alarm before moving the valuable.  
           [0007]    2-way signaling devices extend the capability of monitoring a valuable further by allowing a user to screen signals and get feedback from the valuable. However, these devices are often complex and are undesirably hard to use.  
           [0008]    Scholder, U.S. Pat. No. 5,578,991 discloses a security system for a portable personal computer. The security system includes a sensor which detects when the computer is moved away from an object, such as the surface of a table on which the computer is sitting. The sensor is connected to trigger an alarm.  
           [0009]    Andrews U.S. Pat. No. 5,757,271 discloses a security system for a portable computer. A security device detects whether or not a second electronic device is nearby. In response to a detection that the second electronic device is not nearby a signal is generated indicating that a security violation has occurred. In one embodiment, wireless signals having an effective range equal to the selected proximity are transmitted from the second electronic device to the first electronic device. The security device determines that the first electronic device is not within the selected proximity of the second electronic device in response to a failure to receive the wireless signals.  
           [0010]    D&#39;Angelo, et al. U.S. Pat. No. 5,963,131 discloses a motion sensitive theft detector system for portable articles featuring two way communication between the theft detector unit installed in or affixed to a portable article and a control unit carried by the owner. The theft detector communicates alerts to the control unit allowing the user to screen for false alarms and to trigger an alarm at the portable article when warranted.  
           [0011]    D&#39;Angelo, et al. U.S. Pat. No. 6,133,830 discloses a motion sensitive theft detector system for portable articles featuring two way communication between the theft detector unit installed in or affixed to the portable article and the control unit carried by the owner. The theft detector communicates alerts to the control unit allowing the user to screen for false alarms and to trigger an alarm at the portable article when warranted.  
           [0012]    There remains a need for practical cost effective theft-deterrent devices and methods.  
         SUMMARY OF THE INVENTION  
         [0013]    One aspect of the invention provides a valuables monitoring system. The system comprises a disturbance detection mechanism comprising one or more sensors configured to generate a disturbance signal upon disturbance of an item being monitored; an alarm connected to be triggered by the disturbance signal; and a receiver configured to receive a wireless signal from a remote unit. An alarm inhibition mechanism is connected to selectively inhibit operation of the alarm. The alarm inhibition mechanism includes a mechanism responsive to signals from the remote unit received at the receiver to automatically inhibit the alarm if the received signals indicate that the remote unit is nearby.  
           [0014]    Another aspect of the invention provides a method for monitoring an item. The method comprises providing a base unit attached to the item and a remote unit; detecting a proximity of the remote unit to the base unit and inhibiting an alarm if the remote unit is determined to be nearby the base unit. The alarm is triggered in response to a disturbance of the base unit unless the alarm is inhibited.  
           [0015]    Further aspects of the invention and features of specific embodiments of the invention are described below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    In drawings which illustrate non-limiting embodiments of the invention,  
         [0017]    [0017]FIG. 1 is a block diagram of apparatus according to a basic embodiment of the invention;  
         [0018]    [0018]FIG. 1A is a block diagram of apparatus more fully featured than the apparatus of FIG. 1;  
         [0019]    [0019]FIG. 2 is a flowchart illustrating a process performed at a base unit of one embodiment of the invention;  
         [0020]    [0020]FIG. 3 is a flowchart illustrating a process performed at a remote unit cooperating with a base unit operating under the process of FIG. 2;  
         [0021]    [0021]FIG. 4 is a schematic illustration showing a base unit having a locking mechanism for locking the base unit to an item to be protected;  
         [0022]    [0022]FIG. 5 is a flow chart illustrating a process for turning on a base unit in some embodiments of the invention; and,  
         [0023]    [0023]FIG. 6 is a flow chart illustrating a process for turning on a remote unit and turning off both a remote unit and a corresponding base unit in some embodiments of the invention. 
     
    
     DESCRIPTION  
       [0024]    Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.  
         [0025]    The invention will be described with reference to example systems and methods for alerting a person when an item in their charge is tampered with and/or moved. Apparatus  10  according to a general embodiment of the invention is shown in FIG. 1. A valuable item,  12  for example, a portable computer, is equipped with one or more sensors  13 . Sensors  13  detect disturbance (e.g. movement or tampering) of item  12 . In some embodiments of the invention, sensor  13  comprises one or more tilt sensors, accelerometers, touch sensors, optical sensors or the like.  
         [0026]    An alarm  14  is coupled to receive signal(s) from sensor  13 . The alarm is triggered when sensor  13  generates a disturbance signal which indicates that item  12  is being disturbed (e.g. tampered with and/or moved). The alarm is inhibited when a wireless signal from a remote unit  15  indicates that the remote unit is near to item  12 . In the embodiment of FIG. 1, an alarm inhibition mechanism  16  receives a wireless signal from remote unit  15 . As long as the wireless signal indicates that remote unit  15  is nearby (for example, as long as the signal is stronger than a threshold value) alarm inhibition mechanism  16  inhibits alarm  14 . Alarm inhibition mechanism  16  may comprise, for example, an electronic circuit; a software process being executed by a data processor; or some combination thereof.  
         [0027]    In some embodiments of the invention, apparatus  10  includes a transmitter  17  that transmits a notification signal to a receiver  18  in remote unit  15  when alarm  14  is triggered. In such embodiments, receiver  18  may be connected to trigger an alarm indicator  19  when the notification signal is detected. Alarm indicator  19  may comprise an audible, visual or tactile warning device, for example.  
         [0028]    Apparatus  10  can be used simply. A user can keep remote unit  15  on his or her person. While the user remains near item  12 , alarm inhibition mechanism responds to the proximity of remote unit  15  and inhibits the operation of alarm  14 . The user can move and use item  12  without raising an alarm. If the user leaves the vicinity of item  12 , alarm inhibition mechanism  16  ceases to inhibit the operation of alarm  14 . While the user remains away from the immediate vicinity of item  12 , any disturbance detected by sensors  13  will trigger alarm  14 . If apparatus  10  includes a mechanism for transmitting a notification signal to remote unit  15  then alarm indicator  19  warns the user that an alarm has been triggered, even if the user is not in the immediate vicinity of item  12 .  
         [0029]    An advantage of this embodiment of the invention is that the operation of apparatus  10  is simple for the user. The user does not need to manually arm and disarm apparatus  10  to switch alarm  14  between its enabled and disabled modes.  
         [0030]    The components of apparatus  10  that are collocated with item  12  may be integrated with item  12  or may be combined in a base unit which can be attached to item  12 .  
         [0031]    [0031]FIG. 1A shows a system  20  according to a more fully featured embodiment of the invention. System  20  includes a base unit  21  and a remote unit  22 . Remote unit  22  may be carried by a user. Base unit  21  may be affixed to a valuable to be protected.  
         [0032]    Base unit  21  includes a control circuit, which may conveniently comprise a microcontroller  24 . Microcontroller  24 , may comprise a suitable microcontroller chipset that allows for software programs to be stored and executed. In the alternative, the control circuit could comprise logic circuits which are configured specifically to provide one or more of the functions described herein. Such logic circuits could be provided on an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or by way of discrete components, for example.  
         [0033]    In the embodiment of FIG. 1A, microcontroller  24  includes a clock, a central processing unit (CPU), random access memory (RAM), and read only memory (ROM) which may be on one or more chips. Base unit  21  also includes a motion sensor circuit  25 , an alarm circuit  23 , an ON control  26 , and a two-way wireless communication mechanism.  
         [0034]    In the illustrated embodiment, the communication mechanism comprises an RF transceiver which includes a transmitter  28  and a receiver  27 . The transmitter  27  and receiver  28 , can be provided conveniently by the transmitter and receiver portions of a commercially available RF transceiver. These components could also be made up of discrete components. Any suitable communication protocol may be used for signalling between base unit  21  and remote unit  22 . In some embodiments, digital data is exchanged between base unit  21  and remote unit  22 . In some embodiments data is communicated by sending a low power RF signal that includes preamble data bits that allow other receivers to lock onto the frequency of transmission of transmitter  28 , an identifier comprising a sequence of bits unique to one remote unit  22 , and instruction bits which remote unit  22  can process.  
         [0035]    Motion sensor circuit  25  includes one or more sensors. The sensors may include one or more:  
         [0036]    tilt switches;  
         [0037]    vibration sensors;  
         [0038]    accelerometers;  
         [0039]    proximity detectors;  
         [0040]    capacitive sensors;  
         [0041]    mechanical switches located to change state when the base unit is lifted away from a surface on which it is sitting;  
         [0042]    light detectors; and/or  
         [0043]    other sensors or combinations of sensors capable of generating an output signal indicative that base unit  21  is being moved, tampered with of otherwise disturbed.  
         [0044]    An disturbance signal from motion sensor circuit  25  is provided to microcontroller  24 . Any suitable mechanism may be used to provide the disturbance signal to microcontroller  24 . For example, sensor circuit  25  could be configured to:  
         [0045]    set a flag, for example by writing a value to a data register;  
         [0046]    trigger an interrupt sequence in the microcontroller  24 ;  
         [0047]    set a control line to a current or voltage level indicative of an alarm condition;  
         [0048]    or the like.  
         [0049]    Siren circuit  23 , includes any suitable audible and/or visual alarm generator together with any necessary driving circuits.  
         [0050]    ON control  26 , may comprise a pushbutton or other input mechanism coupled to a circuit which causes base unit  21  to power up.  
         [0051]    Remote unit  22  includes a control circuit. The same general design options available for the control circuit of base  21  are also available for the control circuit of remote unit  15 . In the illustrated remote unit  22  a microcontroller  33  provides control functions.  
         [0052]    Remote unit  22  also includes a notification circuit  34 , an ON/OFF control  31 , a DISARM control  32 , and a two-way wireless communication mechanism compatible with the wireless communication mechanism of base unit  21 . In the illustrated embodiment, the communication mechanism of remote unit  22  comprises a transmitter  30  capable of broadcasting a wireless signal which can be received by receiver  27  of base unit  21  and a receiver  29  capable of receiving signals broadcast by transmitter  28  of base unit  21 .  
         [0053]    The signals exchanged by the wireless communication mechanism are preferably encoded. The use of encoded signals allows several systems  20  to operate in the same vicinity even if the wireless communication mechanisms of the systems operate at the same frequencies. Encoding and decoding of signals exchanged between remote unit  22  and base unit  21  may be performed by microcontrollers  24  and  33  or, in the alternative, by separate encoder/decoder systems. Microcontrollers  24  and  33  may be configured to ignore signals that are not encoded in the manner associated with the corresponding unit  21  or  22 .  
         [0054]    Wireless communications between a remote unit  21  and a base unit  22  may be carried by radio frequency signals. A suitable frequency-hopping algorithm may be used to reduce the likelihood of interference with signals from other systems  20  or other devices operating in a frequency range of the radio frequency signals. Various suitable frequency-hopping systems are known to those skilled in the art of radio frequency communications.  
         [0055]    Notification circuit  34  comprises a device for alerting a user carrying remote unit  22 . Remote unit  22  may include a sound-emitting device such as a speaker or buzzer, a light emitting device, a tactile device, such as a vibrator, and any circuitry necessary to drive the device.  
         [0056]    ON/OFF control  31  and DISARM control  32  each comprise a suitable input mechanism, such as a pushbutton, which can be activated by a user.  
         [0057]    When system  20  is off, it can be turned on by actuating ON control  26  on base unit  21  and actuating ON/OFF control on remote unit  22 . It is noteworthy that, in the illustrated embodiment, there is no control on base unit  21  for turning system  20  off. System  20  can be turned off by actuating ON/OFF control  26  of remote unit  15 . This makes it difficult for a malicious individual to interfere with the proper operation of system  20  by turning off base unit  21 .  
         [0058]    System  20  may include a soft switch mechanism which controls switching both remote unit  22  and the base unit  21  between their active modes and standby modes. The soft switch mechanism may use both software and hardware circuitry to accomplish its task. FIGS. 5 and 6 illustrate methods performed by an example embodiment of such a soft switch mechanism at the base unit and remote unit respectively. As shown in FIG. 5, activating ON control  26  moves process  80  from block  81  to block  82 . Block  82  causes power to be supplied to microcontroller  24  and other circuits of base unit  21 . After process  80  has left block  81 , activating the ON control  26  additional times has no effect. Process  80  then waits to receive an off signal  83  from remote unit  22 . When an OFF signal (encoded in the expected manner) is received by way of receiver  27 , process  80  moves to block  84  which causes power to microcontroller  24  and other circuits of base unit  21  to be being turned off. Base unit  21  can be turned off only by way of remote unit  22 .  
         [0059]    [0059]FIG. 6 illustrates a process  90  which is invoked when remote unit  22  is off and ON/OFF control  31  is actuated by a user in block  91 . Operation of ON/OFF control  31  causes power to be supplied to microcontroller  33  and other circuits of remote unit  22  in block  92 . Process  90  then moves to block  93  where it remains until the user operates ON/OFF control  31  again. Preferably, block  93  requires the user to keep ON/OFF control  31  actuated for at least a short while. This reduces the likelihood that the user could accidentally turn system  20  off.  
         [0060]    When block  93  detects that ON/OFF control  31  has been actuated for a sufficient time, process  90  moves to block  94 . The exact time for which ON/OFF control  31  must be actuated is not critical. The time is chosen to be longer than any anticipated accidental actuations of ON/OFF control  31 . In block  94 , process  90  sends an OFF signal to base unit  21  by way of transmitter  30  (assuming that base unit  21  is on and process  80  is on block  83  the OFF signal causes base unit  21  to turn off). Process  90  then completes at  95  by turning the power off to remote unit  22 .  
         [0061]    When system  20  is operating, programs running on microcontrollers  24  and  33  cause signals to be exchanged periodically between base unit  21  and remote unit  22 . From the signals received at base unit  21 , microcontroller  24  can determine when remote unit  22  is nearby. The signals sent by base unit  21  to remote unit  22  may include signals which indicate that sensor system  25  has detected disturbance. The signals sent by remote unit  22  to base unit  21  may include OFF signals, and/or other control signals.  
         [0062]    During normal operation, each of remote unit  22  and base unit  21  expect to periodically receive a coded signal from the other every so often.  
         [0063]    [0063]FIG. 2 illustrates a flowchart for an operating process  40  performed by microcontroller  24  of base unit  21  in one embodiment of the invention. Process  40  commences at block  41  when microcontroller  24  is either powered up or woken up from a low-power idle mode. Once microcontroller  24  is activated, process  40  proceeds to step  42  where receiver  27  is set to receive mode for a short period of time. While receiver  27  is in receive mode, microcontroller  24  processes any received bits and checks to see if a valid signal from the corresponding remote unit  22  has been received. If such a signal is received then block  43  uses the signal to determine whether or not remote unit  22  is nearby.  
         [0064]    Block  43  may include generating a request signal at transmitter  28  which, when received by remote unit  22  causes remote unit  22  to automatically transmit a ranging signal. The ranging signal may be used by base unit  21  to determine whether or not remote unit  22  is nearby as described above.  
         [0065]    Various methods can be used to determine whether remote unit  22  is nearby. These include:  
         [0066]    Sending a low power ranging signal from remote unit  22  to base unit  21 . If the low power signal is successfully received then block  43  concludes that remote unit  22  is nearby. If the low power signal is not received then block  43  concludes that remote unit  22  is not nearby. The power of the low-power signal sent by remote unit  22  and/or the sensitivity of receiver  27  may be set to adjust the maximum distance at which the low-power signal can be received by base unit  21 . The low power ranging signal may have the same or a different power level than other signals exchanged between base unit  21  and remote unit  22 .  
         [0067]    At base unit  21  measuring the strength of a signal originating from remote unit  22  and comparing the measured signal strength to a threshold value. Since signal strength falls off with distance, the remote unit  22  can be considered to be nearby if the signal strength exceeds the threshold value. Any or all of the threshold value, the strength of the transmitted signal, and an attenuation of the received signal prior to measuring the signal strength may be varied to adjust the maximum distance at which the received signal strength can exceed the threshold.  
         [0068]    If block  43  determines that the remote unit is nearby then process  40  proceeds to sleep  44 . In the alternative, if process  40  does not determine that the remote unit  22  is nearby then process  40  proceeds to block  45 . In block  45 , base unit  21  sends a reminder signal to remote unit  22  the reminder signal is sent by way of transmitter  28 . When remote unit  22  receives the reminder signal, microcontroller  33  causes a reminder action to be generated at remote unit  22 . The reminder action may comprise generating a tone or other audible signal, flashing or blinking an indicator light, vibrating slightly or the like. The reminder action reminds the person carrying remote unit  22  that the base unit  21  and associated valuable have been left behind. This feature enables the user to be notified with a subtle beep or visual queue once they are separated from their valuable, in case they simply forgot to bring it with them.  
         [0069]    Process  40  now proceeds to block  47 . In block  47  microcontroller commences monitoring the output of sensor system  25  for signals indicative that base unit  21  has been moved or tampered with.  
         [0070]    If no motion or tampering is detected, process  40  goes back to sleep in block  44 .  
         [0071]    If motion or tampering is detected in block  47 , base unit  21  sends a notification signal by way of transmitter  28 . The notification signal is received by remote unit  22  if remote unit  22  is not too far away. When remote unit  22  receives the notification signal, remote unit  22  generates a notification action distinct from the reminder action. The notification action may comprise an audio, visual or tactile signal or a combination thereof.  
         [0072]    Base unit  21  also initiates a timer (block  49 ) in response to detecting the motion or tampering. The timer provides the person who has remote unit  22  with an opportunity to disarm base unit  21  before alarm  23  sounds, and thereby avoid an undesired alarm from being issued by base unit  21 . Process  40  then places base unit  21  in receive mode (block  50 ) and loops around blocks  51  and  52  until the timer expires or a DISARM signal is received from remote unit  22 . If block  51  detects a DISARM signal before the timer expires then process  40  proceeds to sleep  44 . If block  52  determines that the timer has expired then process  40  proceeds to block  53  which activates siren  23 .  
         [0073]    After turning on siren  23 , process  40  causes receiver  27  to listen for a DISARM signal from remote unit  22  in block  55 . When the DISARM signal is received then base unit  21  turns siren  23  off at block  56 . After turning the siren off, microcontroller  24  and transceiver ( 27  and  28 ) enter sleep mode once again at  44 .  
         [0074]    Process  40  operates on base unit  21  which operates in conjunction with remote unit  22 . A software program executing on microcontroller  33  may coordinate the operation of remote unit  22 . A process  60  that may be followed by such a program is illustrated in Figure FIG. 3. Process  60  commences at block  61  where microcontroller  33  is either powered up or woken up from a low power idle mode.  
         [0075]    Process  60  then proceeds to block  62  wherein it controls transmitter  30  to transmit a RF signal at low power and then proceed immediately to place receiver  29  into receive mode at block  63 . If, during this receive mode, receiver  29  detects a reminder signal from base unit  21 , as indicated by block  64  then process  60  proceeds to block  65  which generates the reminder action (e.g. a short indicator from notification circuit  34 ). Process  60  then proceeds to block  66  which causes microcontroller  33  to go to sleep  66 .  
         [0076]    If block  67  determines that a notification signal has been received (i.e a signal indicating that movement or tampering have been detected at base unit  21  then process  60  proceeds to block  68 . At block  68 , the notification action is performed (e.g. notification circuit  34  is turned fully on).  
         [0077]    After the notification action has been initiated, process  60  checks in block  69  to see if the user has actuated DISARM control  32 . If so, then a DISARM signal is sent by way of transmitter  30  at block  70 . The notification action is discontinued at block  71 . If block  69  does not detect that the user has actuated DISARM control  32  then process  60  remains at block  69 .  
         [0078]    Base unit  12  may be associated with a valuable item to be protected in any of various ways. For example, in various embodiments:  
         [0079]    Base unit  21  includes a lock which allows it to be physically attached to devices like laptops, liquid crystal display monitors, and projectors. The lock may engage a security slot (one example being a Kensington slot), a PC card interface of a computer, a PC Universal Serial Bus port of a computer, a floppy disk drive of a computer or the like.  
         [0080]    Base unit  21  is integrated into a valuable item to be protected—for example as part of a motherboard of a laptop computer. or  
         [0081]    Base unit  21  is affixed to a valuable item to be protected with a fastening means such as screws, bolts, rivets, an adhesive, or the like.  
         [0082]    [0082]FIG. 4 shows a base unit  21  having a locking mechanism  19  according to one embodiment of the invention. Locking mechanism  19  may comprise a cable lock and may be adapted to lockingly engage a security slot of the type sometimes provided on laptops, LCDs, and LCD projectors and the like.  
         [0083]    Base unit  21  and remote unit  22  may each have an internal power supply  129 , typically a battery. In many applications of the invention it is desirable to make base unit  21  and remote unit  22  lightweight for easy portability. In such cases power management is important because there is a limit to the capacity of lightweight batteries. Power consumption can be minimized, by having microcontrollers  24  and  33  spending significant proportions of the time in sleep modes.  
         [0084]    There are a wide range of suitable mechanisms for causing a microcontroller to wake up periodically from a low power (or “sleep”) mode to perform a necessary process and then return to the low power mode. For example:  
         [0085]    A software timer may operate while the processor is in sleep mode. The software timer may interrupt the microcontroller ( 24 ,  33 ) when it is time to wake up.  
         [0086]    A separate timer, such as a digital logic counter coupled to a system clock may be connected to pass an elapsed time signal to the microcontroller or to another part of the circuit. For example, a microcontroller might set the timer to expire after a certain period of time. Upon the time period ending the timer could cause a flag to be set or send a signal to some circuitry indicating that time has expired.  
         [0087]    By operating microcontrollers and/or other circuits at full power only some of the time, overall power consumption can be significantly reduced. In some cases, power can be on less than half of the time, and in another case it can be on for only a quarter of the time, and in yet another case can be on for less than an eighth of the time, and so on.  
         [0088]    Power can further be conserved by operating transceivers of the base unit and remote unit to exchange information according to a protocol that minimizes the amount of time that the transceivers are operating and especially minimizes transmitting operations.  
         [0089]    Certain implementations of the invention comprise computer processors which execute software instructions which cause the processors to perform a method of the invention. For example, one or more processors in a base unit may implement the methods of FIG. 2 by executing software instructions in a program memory accessible to the processors. The invention may also be provided in the form of a program product. The program product may comprise any medium which carries a set of computer-readable signals comprising instructions which, when executed by a computer processor, cause the data processor to execute a method of the invention. Program products according to the invention may be in any of a wide variety of forms. The program product may comprise, for example, physical media such as magnetic data storage media including floppy diskettes, hard disk drives, optical data storage media including CD ROMs, DVDs, electronic data storage media including ROMs, PROMS, EPROMS, flash RAM, or the like or transmission-type media such as digital or analog communication links.  
         [0090]    Where a component (e.g. a software module, processor, assembly, device, circuit, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.  
         [0091]    As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example:  
         [0092]    Alarm inhibition circuit  16  could inhibit triggering of alarm  14  or, in the alternative, could inhibit the effect of alarm  14 , for example, by silencing audible warnings and/or disabling visual alarm displays provided by alarm  14 .  
         [0093]    In addition to sounding an alarm upon a possible theft attempt, base unit  21  could be configured to activate or protect the valuable further by locking down peripherals of a laptop, encrypting data, connecting to a global positioning system in order to track the valuable or the like.  
         [0094]    The invention is not limited to use in protecting inanimate valuable items. The methods and components described herein may also be used for monitoring pets or children. For example, a base unit  21  could be incorporated into a bracelet to be worn by a child or a collar to be worn by a pet.  
         [0095]    The signals exchanged between a base unit and a remote unit do not need to be radiofrequency signals. Other types of wireless signals, such as ultrasonic signals could be used in the alternative.  
         [0096]    It is not mandatory that the same type of signals used to carry information (e.g. OFF signals, DISARM signals, REMINDER signals, NOTIFICATION signals) be used to determine when remote unit  22  is near to base unit  21 . For example, an ultrasonic signal could be used for ranging while radiofrequency signals are used to carry information receivers in the base and/or remote units may include receivers for different signal types.  
         [0097]    Signals used to carry information between a base unit and remote unit may have different strengths, frequencies, formats etc. from signals used to determine when the corresponding remote unit is nearby to a base unit. In some embodiments low strength ranging signals are used for determining whether the remote unit is nearby to the base unit and some or all of the information carrying signals have significantly greater ranges than the ranging signals.  
         [0098]    Ranging signals could also be used to carry information between a base unit and a remote unit or vice versa.  
         [0099]    In some of the embodiments described above, a low strength ranging signal is sent from the remote unit to the base unit. The base unit knows that the remote unit is nearby if it receives the low strength ranging signal. The invention could also be practised by sending a low strength ranging signal from the base unit to the corresponding remote unit. The remote unit could be configured to generate a reply signal upon detecting the low strength ranging signal. In such embodiments the base unit would know that the remote unit is nearby if it receives reply signals in response to its low strength ranging signals.  
         [0100]    ON/OFF control  31  may be replaced with separate ON and OFF controls.  
         [0101]    The frequencies of signals used by a system do not need to be fixed. The system may have the capability to vary the operating frequency to prevent interference from other products working in the same RF band or signal frequency.  
         [0102]    Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.