Abstract:
An apparatus includes a device which is capable of performing a function, and which is responsive to receipt of a predetermined wireless signal for nondestructively rendering itself incapable of thereafter performing the function. In one form of the invention, the capability of the device to perform the function can be restored by the occurrence of a secure event originating externally of the device. In a different form of the invention, the device includes a memory, and information stored in the memory is erased in order to render the device incapable of performing the function.

Description:
BACKGROUND OF THE INVENTION 
   Efforts are made to keep certain equipment such as sophisticated military weapons out of the hands of unauthorized users, including terrorists and military adversaries. Nevertheless, these weapons and equipment sometimes do come to be in hostile control. This may occur through theft, or through unauthorized sale. Alternatively, weapons or equipment may be sold to a foreign nation at a time when the nation is considered to be an ally, but that nation may subsequently come to be considered an adversary, for example due to a coup or some other internal political shift. Still another consideration is that it is sometimes difficult to determine who will actually be the true and ultimate recipient of weapons or equipment that are involved in a particular sale. 
   The fact that equipment or a weapon is present in hostile hands is a problem, not only when it is known that the particular weapon or item of equipment is in hostile hands, but also when it not yet known that the equipment or weapon has passed into hostile hands. Traditional attempts to avoid this type of problem have included strict export restrictions regarding which weapons and equipment can be exported or sold, and to whom. While these export restrictions have been helpful to some degree, they have not been satisfactory in all respects. 
   SUMMARY OF THE INVENTION 
   From the foregoing, it may be appreciated a need has arisen for a method and apparatus for limiting unauthorized or undesirable use of weapons or equipment. According to the present invention, a method and apparatus are provided to address this need, and involve operating a device capable of performing a function so that, in response to receipt by the device of a predetermined wireless signal, the device is rendered incapable of thereafter performing the function. According to one form of the invention, the capability of the device to perform the function can be restored in response to the subsequent occurrence of a secure event originating externally of the device. According to a different form of the invention, information is stored in a memory, a processor helps perform the function in dependence on the information in the memory, and the information is erased from the memory in order to render the device incapable of performing the function. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention will be realized from the detailed description which follows, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram of a system which embodies the invention and which permits an authority to remotely locate and/or disable equipment such as a military weapon; 
       FIG. 2  is a block diagram showing additional detail regarding the internal structure of an item of equipment which is a component of the system of  FIG. 1 ; and 
       FIG. 3  is a flowchart showing a sequence of operations carried out by a processor which is a component of the item of equipment shown in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a diagrammatic view of an apparatus which is a system  10  that embodies aspects of the present invention. The system  10  includes an item of equipment  12 , which has an antenna  13 . In the disclosed embodiment, the item of equipment  12  is a military weapon, such as a mobile rocket launcher of the type that can be manually carried, or a larger mobile rocket launcher of the type mounted on a vehicle. However, the present invention is not limited to a weapon and/or a military context, but could readily be utilized for a variety of different types of devices in a variety of other applications. 
   The system  10  further includes a control center  16 , which has an antenna  17 . In the disclosed embodiment, the control center  16  is a military headquarters. However, as noted above, the present invention is not limited to a military context, and the control center  16  could thus be part of a commercial entity, or some other form of entity. 
   The system  10  includes a satellite  21 , and a high-altitude airplane  22 , both of which serve as a relay for wireless signals being transmitted between the control center  16  and the equipment  12 . In particular, as indicated diagrammatically by the broken lines at  26  and  27 , the satellite  21  can relay wireless signals which are being transmitted between the control center  16  and the equipment  12 . Similarly, as indicated diagrammatically by the broken lines at  28  and  29 , the airplane  22  has equipment that can relay wireless signals which are being transmitted between the control center  16  and the equipment  12 . For clarity,  FIG. 1  shows a single satellite  21  and a single airplane  22 , but the system  10  can include a plurality of satellites  21  and/or a plurality of airplanes  22 , which each cover various different portions of the surface of the earth. 
   The system  10  includes a plurality of towers that support antennas, two of which are shown at  37  and  38  in  FIG. 1 . The antennas on these towers are operatively coupled to the control center  16  through a cable  36 . However, the control center  16  could alternatively be coupled to the antennas on the towers  37  and  38  in some other manner, for example through wireless signals relayed through the satellite  21  and/or the airplane  22 . Wireless signals can be transmitted between the equipment  12  and the antennas on each of the towers  37  and  38 , for example as indicated diagrammatically by the broken lines at  43  and  44 . Although not shown in the drawings, it would be possible to have a mobile ground unit with an antenna which was functionally comparable to the antennas on the towers  37  and  38 , where the mobile ground unit would communicate with both the control center  16  and the equipment  12  through respective wireless transmissions. 
   Although the satellite  21 , the airplane  22  and the towers  37  and  38  serve as respective parts of the system  10 , they can simultaneously serve other functions. For example, the satellite  21  and the airplane  22  may each relay wireless signals for a different type of system with a different function, such as wireless signals that carry telecommunications information. Similarly, the towers  37  and  38  may also serve other functions, and may for example be part of a cellular telephone network. 
   At any given point in time, the equipment  12  may not be in a scenario where it is served by all types of wireless communication support. For example, since the equipment  12  is mobile, it may be moved to an undeveloped part of the globe where there is little or nothing in the way of land-based antennas like those supported by the towers  37  and  38 , but where communication is possible through a satellite  21 , and/or through a high-altitude airplane  22 . As a different example, the equipment  12  could also be moved to a major urban area, where there are many land-based antennas of the type supported on the towers  37  and  38 , and where there is service from a satellite such as that shown at  21 , but where no airplane  22  is currently present. 
     FIG. 1  shows several ways in which wireless signals can be transmitted to or from the equipment  12 , for example by way of the satellite  21 , by way of the airplane  22 , or by way of land-based antennas such as those on the towers  37  and  38 . These various techniques are presented by way of example, and are not to be considered limiting. The invention contemplates that wireless signals could be transmitted to or from the equipment  12  in any other suitable manner. 
   Before describing certain aspects of the system  10  in detail, a brief overview of the operation of the system  10  will be provided in order to facilitate a better understanding of the details. More specifically, it is initially assumed that the equipment  12  is in the hands of a military adversary. This may be the result of a situation in which the equipment  12  was obtained by a terrorist or other adversary through proper or improper means. Alternatively, this may be the result of a situation in which the equipment was sold to a nation that was considered to be a friendly ally at the time of the sale, but that later came to be considered an adversary, for example due to political changes at the international level, or through a coup or other political upheaval within the foreign nation. 
   A first consideration is that it may be helpful to know the current location of the equipment  12 . In fact, knowledge of the current location of the equipment  12  may be a significant factor in identifying a situation where the equipment  12  has come to be in the possession of an adversary. To this end, the equipment  12  is designed so that, when it is turned on, it automatically transmits a wireless signal containing a code that uniquely identifies the equipment. This transmission is encrypted, for example using encryption techniques of a known type, in order to prevent an adversary from generating wireless signal which emulate the wireless signals that are transmitted by the equipment  12 . 
   This transmission can be used to determine the current location of the equipment  12 . For example, where the signal is received by two or more different antennas at spaced locations, such as the antennas on the two towers  37  and  38  in  FIG. 1 , the location of the equipment can be determined through known triangulation techniques. Where the signal is received by only a single antenna, the location of the equipment can still be roughly determined on the basis of the transmission range of the equipment. In other words, if the equipment can transmit a signal a specified distance, then the equipment should be within circular region around the receiving antenna which has a radius equal to the specified distance. The location of the equipment can be determined to an accuracy of about  10  km, or better. The signal which the equipment  12  broadcasts at power-up can also serve as a trigger for the control center  16  to send that item of equipment any wireless messages destined for it that may have been queued up while its power was turned off. 
   After the equipment  12  has been turned on, the control center  16  can broadcast a wireless inquiry or interrogation signal through all available wireless paths, and the equipment  12  will then respond to each such interrogation signal by transmitting a wireless signal that is equivalent to the signal which it transmits when its power is turned on. Each time the equipment  12  transmits this wireless signal, the signal will be received through one or more wireless links and will be forwarded to the control center  16 . The control center  16  can use this information not only to identify the equipment  12 , but also to identify its location. If the control center does not receive a wireless signal from a particular item of equipment in response to several interrogation commands, an appropriate person or authority is notified. 
   Assuming a determination is made that the particular item of equipment  12  is now in the hands of an adversary, the control center  16  can send through any or all of the wireless paths in  FIG. 1  a predetermined wireless signal which is encrypted and which causes the equipment  12  to disable selected functional capabilities (such as its capability to function as a weapon). These functional capabilities are disabled in a manner so that the equipment  12  cannot be restored to its normal operational capability without some external device or information which is controlled by the control center  16 . 
   Thus, for example, control center  16  can use a predetermined and encrypted wireless signal to disable the capability of the equipment  12  to function as a weapon, and this capability cannot be restored unless the control center  16  decides to restore it, for example by transmitting a further encrypted signal containing information which the equipment  12  needs in order to restore its capability to function as a weapon. The wireless signals are appropriately encrypted, so that an adversary cannot generate these signals for purpose of disabling comparable equipment  12  which is still under control of the control center  16  and thus available for use against the adversary, or for the purpose of restoring the functional capability of a disabled weapon which is in the possession of the adversary. 
   To the extent that an adversary has possession of the equipment  12  under circumstances where the equipment  12  has not yet been disabled by the control center  16 , there will be motivation for the adversary to try to tamper with the equipment  12  in a manner which prevents the equipment  12  from disabling itself in response to a wireless command from the control center  16 . Accordingly, the equipment  12  has been designed to have the capability to detect tampering. In the event that the equipment  12  finds that tampering may have occurred, the equipment  12  automatically disables itself in essentially the same manner as if it had received a wireless command to disable itself, for example by disabling its capability to function as a weapon. 
   To this point, the present discussion of operation has been based on the assumption that the equipment  12  is in the possession of an adversary. It is alternatively appropriate to consider the situation where the equipment  12  is presently in friendly hands, rather than the hands of an adversary. In this regard, and as discussed above, the equipment  12  normally transmits an identification signal each time its power is turned on, and each time it subsequently receives an interrogation signal. However, if the equipment  12  is in friendly hands, and if it is being used for a mission or operation, wireless transmissions by the equipment  12  could be undesirable. In particular, wireless transmissions by the equipment  12  could be intercepted and evaluated by an adversary, thereby permitting the adversary to detect the presence of the equipment and identify its location, for example through triangulation, even if the adversary did not have the capability to decrypt the encrypted information which is embedded present in the wireless signal. 
   Detection of the presence and/or location of the equipment  12  would typically give away to an adversary the presence and/or position of the friendly soldiers or other persons who are using the equipment  12 , which is obviously undesirable. Accordingly, where the equipment  12  is known to currently be in friendly hands, the control center  16  can send to a particular item of equipment  12  a wireless command which instructs that item of equipment  12  to cease all wireless transmissions, until such time as the equipment  12  receives a further wireless command which tells the equipment  12  to resume wireless transmissions. As an alternative to completely inhibiting the equipment  12  from transmitting any wireless signals, the equipment  12  could be provided with transmission hardware having a low probability of detection, such as a highly directional antenna. 
   Turning now in more detail to the equipment  12 ,  FIG. 2  is a block diagram showing relevant aspects of the internal configuration of the equipment  12 . As shown in  FIG. 2 , the equipment  12  includes an equipment control circuit  61 , which produces control signals  62  that control operational capabilities of the equipment  12 . For example, where the equipment  12  is a mobile rocket launcher, the control signals  62  would include signals coupled to not-illustrated structure that controls the capability of the equipment  12  to effect the launch of a rocket. As shown in  FIG. 2 , the equipment control circuit  61  includes a processor  63  which is a known type of processor, and includes random access memory (RAM)  66  in which the processor  63  can store the software it is currently executing, as well as data which the processor  63  is manipulating under program control. The software executed by the processor  63  is stored in an electrically erasable programmable read only memory (EEPROM)  67 , and after a reset, for example when power is turned on, the processor  63  copies the software from the EEPROM  67  to the RAM  66 , and then executes the software from the RAM  66 . The EEPROM  67  is embedded in an integrated circuit  68 . In the disclosed embodiment, the information stored in the EEPROM  67  includes an operating system  71  and an application program  72 , which are both copied to the RAM  66  and then executed by the processor  63 . 
   The integrated circuit  68  includes not only the EEPROM  67 , but also a disable control circuit  76 . By providing both the disable control circuit  76  and the EEPROM  67  within a single integrated circuit, they cannot be easily separated for the purpose of circumventing security features of the equipment  12  which are discussed later. The disable control circuit  76  includes a processor  81 , a read only memory (ROM)  82 , and a RAM  83 . At least one of the ROM  82  and RAM  83  is non-volatile memory, which can store information through a power outage. The processor  81  executes a program which is stored in the ROM  82 , and uses the RAM  83  to store data that the processor  81  is manipulating under program control. 
   The disable control circuit  76  has the capability to selectively erase all or a part of the information stored in the EEPROM  67 , as indicated diagrammatically at  86 . The disable control circuit  76  also has the capability to load information into the EEPROM  67 , as indicated diagrammatically at  87 , for example to restore a portion of the information in EEPROM  67  which was previously erased. Moreover, the disable control circuit  76  has the capability to reset the equipment control circuit  61 , including the processor  63  in the circuit  61 , as indicated diagrammatically at  88 . When the disable control circuit  76  resets the equipment control circuit  61 , the processor  63  in the circuit  61  has to “reboot”, which includes copying software that the processor  63  is to execute from the EEPROM  67  to the RAM  66 . 
   The equipment  12  also includes a transmitter/receiver circuit  91 , which is operationally coupled to the antenna  13  and to the disable control circuit  76 . The transmitter/receiver circuit  91  uses the antenna  13  to transmit and receive wireless signals that are encrypted. The encryption is effected using a suitable encryption technique of a type which is known to persons skilled in the art. The sophistication of the encryption technique can be selected to satisfy the particular application in which the equipment  12  is being used. 
   For example, in the disclosed embodiment, the equipment  12  is a form of military weapon, and the encryption technique would likely have a level of sophistication appropriate for a military application. On the other hand, in some other context, such as a commercial context, a known encryption technique of less sophistication would be suitable. The present invention is compatible with a wide range of encryption techniques, and it is not necessary to present the specific details of any particular encryption technique here in order to convey an understanding of the present invention. 
   The equipment  12  includes a tamper detection section  92 , which is operatively coupled to the equipment control circuit  61 , the transmitter/receiver circuit  91 , and the antenna  13 , and which is capable of detecting circumstances in which a person has tampered with portions of the equipment  12 . In this regard, the tamper detection section  92  can perform a number of checks of the type which are known in the art and are typically used by a processor to perform a power-on self test (POST) of the circuit that contains the processor. For example, the processor may perform a checksum and/or some other type of error detection analysis on computer program code and data stored in various memories. As another example, the processor may route predetermined data through various data paths in the circuitry, and then check the resulting data to verify that it has an expected value. As still another example, the tamper detection section  92  can check the impedance and/or resistance of certain circuit elements, such as the antenna  13 , in order to verify that they are present and functioning properly. Various other types of checks of the hardware and software can be carried out in order to detect the presence of tampering. In the event that the tamper detection section  92  detects tampering of any type, it uses a line  96  to supply a tamper detect signal to the disable control circuit  76 . 
   In operation, when the equipment  12  is turned on, the tamper detection section  92  checks for any kind of tampering that it is capable of detecting, including tampering that may have taken place while power was turned off. If it detects any tampering, then it uses the line  96  to send a tamper detect signal to the disable control circuit  76 . The processor  81  in the disable control circuit  76  can also check for certain types of problems. For example, if the processor  81  does not receive a valid wireless signal directed specifically to the equipment  12  at least once every three days, the processor  81  can flag the absence of a timely wireless signal as a problem to be treated the same as a determination that there has been tampering. For the moment, it is assumed for purposes of the present discussion that the tamper detection section  92  does not detect any evidence of tampering, that that equipment  81  has received at least one valid wireless signal within the last three days, and that the circuitry shown in  FIG. 2  thus comes up and runs in a normal operational mode. 
   Assuming that the equipment  12  has not been instructed to inhibit all wireless transmissions (in a manner discussed later), then after power to the equipment  12  has been turned on, the disable control circuit  76  will cause the transmitter/receiver circuit  91  to transmit through the antenna  13  an encrypted wireless message, which includes a unique identification of the particular piece of equipment  12 , and which may include other status information regarding the equipment  12 , such as whether any tampering has been detected. After that, the equipment  12  may from time to time receive through the antenna  13  an encrypted wireless message which asks the equipment  12  to transmit the wireless signal, and in response the equipment  12  will again transmit the encrypted wireless message containing its identification and status information (unless transmissions have been disabled). 
   If the equipment  12  is in friendly hands and is known to be in circumstances where it would be undesirable for it to transmit any wireless message, the equipment  12  can be sent an encrypted wireless message which is received through the antenna  13  and the transmitter/receiver circuit  91 , and which causes the disable control circuit  76  to inhibit any further wireless transmissions through the circuit  91  and the antenna  13 . The processor  81  stores in nonvolatile memory, for example at  82  or  83 , an indication that wireless transmissions are currently inhibited. Then, if power for the equipment  12  is turned off and back on, the equipment  12  will remember that it has been instructed not to transmit any wireless signals. Eventually, the equipment  12  can be sent a further wireless message which is received through the antenna  13  and receiver circuit  91 , and which instructs the equipment  12  that it can resume transmitting wireless messages. 
   Circumstances may arise in which the authority in charge of the control center  16  ( FIG. 1 ) may decide that the equipment  12  is in the possession of an adversary or other unauthorized person and should be disabled. In that event, an encrypted wireless message can be sent to the equipment  12 , and will be received through the antenna  13  and transmitter/receiver circuit  91 . In response to that signal, the disable control processor  76  will use the control capability indicated diagrammatically at  86  to erase all or part of the information stored in the EEPROM  67 . In the disclosed embodiment, the disable control processor  76  erases only a selected portion of the operating system  71 . The processor  63  needs this selected portion of the operating system  71  in order to operate the weapons capability of the equipment  12 . Therefore, by erasing this portion of the operating system  71 , the equipment  12  is deprived of its capability to function as a weapon. The equipment  12  is designed so that the information erased from the EEPROM  67  is not present anywhere else in the equipment  12 . Consequently, it is not possible to restore the capability of the equipment  12  to function as a weapon, unless the equipment  12  receives some form of external input, as discussed later. After erasing part or all of the EEPROM  67 , the processor  81  uses the line  88  to reset the equipment control circuit  61 , so that the processor  63  has to “reboot”, which in turn means that the processor  63  will copy software from the EEPROM  67  to the RAM  66 . As a result, the RAM  66  will end up containing the modified program from the EEPROM  67 , and the missing information in this program will prevent the processor  63  from controlling the weapons capability of the equipment  12 . 
   The immediately preceding discussion explained how the disable control circuit  76  can erase information in the EEPROM  67  in response to a wireless signal received through the antenna  13  and the circuit  91 . Alternatively, in the event that the tamper detection section  92  detects any form of tampering, either at power-up or during normal operation of the equipment  12 , the tamper detection section  92  sends a tamper detect signal on line  96  to the disable control circuit  76 , which causes the disable control circuit  76  to in turn erase information in the EEPROM  67 , in the same manner as where the disable control circuit  76  receives a disable command through the antenna  13  and the circuit  91 . Moreover, if the processor  81  detects a situation in which it has not received for at least three days a valid wireless signal directed specifically to the equipment  12 , the processor  81  will erase information in the EEPROM  67  in the same manner as if it had received from the tamper detection section  92  an indication that tampering had been detected. 
   In a situation where the disable control circuit  76  has erased a portion of the information in EEPROM  67 , due to receipt of a wireless command, due to detection of tampering, or due to a determination by the processor  81  that the equipment  12  had not received a valid wireless signal for at least three days, the equipment  12  is rendered incapable as functioning as a weapon, as discussed above. In order to restore the capability of the equipment  12  to function as a weapon, a further encrypted wireless message can be sent to the equipment  12 , and will be received through the antenna  13  and the transmitter/receiver circuit  91 . This wireless message, or at least one subsequent related wireless message, will include encrypted replacement information equivalent to the information previously erased from the EEPROM  67 . The disable control circuit  76  will then, as indicated diagrammatically at  87 , reload the erased portion of the EEPROM  67  with this replacement information. One reason that the disclosed embodiment erases only a selected portion of the information in the EEPROM  67 , rather than all information in the EEPROM  67 , is to reduce the amount of encrypted replacement information that must be received by the equipment  12  in wireless messages in order to restore the equipment  12  to its normal operational status. 
     FIG. 3  is a flowchart showing a sequence of operations carried out by the processor  81  of the disable control circuit  76 . When power to the equipment  12  is turned on, processing starts at block  111  and proceeds to block  112 . In block  112 , the processor  81  checks to see whether it has previously received a command indicating that the equipment  12  is not to transmit any wireless signals. If so, then control proceeds to block  116 . Otherwise, at block  113 , the processor  81  transmits through the circuit  91  an encrypted wireless message which includes information such as a unique identification of the equipment  12 , and status information such as whether a portion of the information in EEPROM  67  has been erased. From block  113 , control proceeds to  116 . 
   In block  116 , the processor  81  and the tamper detection section  92  cooperatively check to see whether there is any evidence of tampering with relevant portions of the equipment  12 . As discussed above, this could include checks of the resistance or impedance of certain portions of the hardware, diagnostic testing of certain portions of the hardware, diagnostic checks of relevant software, and so forth. In addition to checking for tampering, the processor  81  evaluates whether it has received within the last three days a valid wireless signal directed specifically to the equipment  12 . Control then proceeds to block  117 , where the processor  81  determines whether any tampering has been detected, or whether the processor determined that no valid wireless signal had been received within the last three days. 
   If no tampering has been detected, and if a valid wireless signal has been received within the last three days, then control proceeds to block  121 . But if tampering has been detected, or if no valid wireless signal has been received within the last three days, control proceeds to block  118 , where the processor  81  erases a selected portion of the operating system  71  stored in the EEPROM  67 , and then uses the line  88  to reset the equipment control circuit  61 . The reset causes the processor  63  to reboot and thus reload the RAM  66  from the EEPROM  67 . As a result of the missing information in the EEPROM  67 , this effectively disables the ability of the equipment control circuit  61  to cause the equipment  12  to function as a weapon, as discussed above. Moreover, as discussed above, there is nothing within the equipment  12  itself which would permit this erased portion of the operating system  71  to be regenerated. From block  118 , control proceeds to block  121 . 
   In block  121 , the processor  81  checks to see if it has received any wireless signal through the antenna  13  and transmitter/receiver circuit  91 . If not, then control returns to block  116 . In essence, the processor  81  is in a loop, in which it waits for a wireless signal which is directed specifically to the equipment  12  and which contains encrypted information, and in which it also continuously checks for any tampering. 
   When a wireless signal is eventually received, control will proceed from block  121  to block  122 , where the processor  81  checks whether the received wireless signal is requesting that the particular item of equipment  12  transmit an encrypted wireless signal that includes information such as a unique identification of the equipment  12 , and current status information. If the received signal is such an interrogation command, control proceeds from block  122  back to block  112 , so that transmission of the requested wireless signal will be effected at block  113  (unless transmissions have been disabled). On the other hand, if it is determined in block  122  that the received wireless signal is not an interrogation command, control proceeds from block  122  to block  123 . 
   In block  123 , the processor  81  checks to see whether the received wireless signal is a command instructing it to erase at least a portion of the EEPROM  67 . If so, control proceeds to block  126 , where at least a portion of the EEPROM  67  is erased in a manner equivalent to that described above for block  118 . The processor  81  then uses the line  88  to reset the equipment control circuit  612 , and the reset causes the processor  63  to reboot and thus reload the RAM  66  from the EEPROM  67 . As a result of the missing information in the EEPROM  67 , this effectively disables the ability of the equipment control circuit  61  to cause the equipment  12  to function as a weapon, as discussed above. Control then proceeds from block  126  back to block  116 . 
   If it is determined at block  123  that the received wireless signal is not a command to erase part of the EEPROM  67 , then control proceeds from block  123  to block  127 , where the processor checks to see whether the received wireless signal is a command to restore information previously erased from the EEPROM  67 . If so, then the received wireless signal, or some subsequent related wireless signals, will include replacement information that is to be loaded into the EEPROM  67  in place of the information which was previously erased. Control proceeds from block  123  to block  126 , where the processor  81  reloads the erased portion of the EEPROM  67  with the replacement information, as indicated diagrammatically at  87 . From block  126 , control proceeds back to block  116 . 
   If it was determined at block  127  that the received wireless signal is not a command to restore information to the EEPROM  67 , then control proceeds from block  127  to block  131 . In block  131 , the processor  81  checks to see if a received wireless signal is a command instructing the processor  81  to inhibit all wireless transmissions from the equipment  12  until further notice. If so, then control proceeds to block  132 , where the processor  81  sets a flag in a nonvolatile memory  82  or  83  in order to indicate that wireless transmissions are disabled, and then proceeds to block  116 . 
   If it is determined at block  131  that the received wireless signal is not a command to disable wireless transmissions, then control proceeds to block  133 , where the processor  81  checks to see if the received wireless signal is a command to enable wireless transmissions. If not, control proceeds to block  116 . Otherwise, control proceeds to block  136 , where the processor  81  resets the flag that controls the transmission of wireless signals, so that the equipment  12  is enabled to transmit wireless signals. Control then returns to block  116 . 
   In a not-illustrated variation of the disclosed embodiment, the blocks  127  and  128  in  FIG. 3  can be omitted, such that the erased portion of the EEPROM  67  cannot be restored by the technique of transmitting replacement information to the equipment  12  in the form of wireless signals. Instead, the equipment  12  would need to be returned to a factory or a service center, where technicians would restore the functionality that was disabled through erasure of part of the information in the EEPROM  67 . 
   The present invention provides a number of technical advantages. One such technical advantage is that an authority can remotely locate and disable military or other equipment which the authority has deemed to be in unauthorized or undesirable use. A related advantage is that the disabling of the equipment can occur without the consent or knowledge of a person who currently has possession of the equipment. Still another advantage is that, once the equipment is disabled, its functionality cannot be restored without appropriate action by an appropriate authority. 
   Another advantage is that the location of military or other equipment can be determined in a relatively accurate manner. Still another advantage is that the present invention adds little or no significant cost to existing designs for most types of equipment. Yet another advantage is realized by provision of the capability to detect tampering with the equipment, such as tampering intended to override the disabling feature, and provision of the capability to automatically actuate the disabling feature in response to the detection of tampering. Another feature involves provision of the capability to detect a situation in which the equipment  12  had not received a valid wireless signal for a specified time interval, and provision of the capability to automatically actuate the disabling feature in response to detection of either tampering or the lack of receipt of a valid wireless signal for a predetermined time interval. 
   Although one embodiment has been illustrated and described in detail, it will be understood that various substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.