Abstract:
A remote control (RC) device and base station of a security system communicate automatic passive remote control commands at a lower power level than the level used to transmit other information. Lowering the power level of the passive remote control transmissions from the RC device decreases energy consumption and improves battery life. Additionally, the range of the automatic commands is shortened, potentially avoiding some unwanted door lock activations, security system arming and disarming events, and similar occurrences. At the same time, the range of the user-entered commands does not suffer. In embodiments where the RC device sends passive remote control commands in response to periodic interrogatory transmissions from the base station, the power level of the interrogatory transmissions is lower than the power level of other transmissions. Thus, frequency of unwanted door lock activations and arming/disarming events is decreased, while the range of other transmissions from the base station is unchanged.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to security, alarm, and convenience systems, and, more particularly, to remotely controlled vehicular and other security systems with automatic disarming, deactivation, passive remote control, keyless entry, and similar features.  
       BACKGROUND  
       [0002]     Security and alarm systems are known. Security systems are often used to secure a perimeter or an object against theft, tampering, vandalism, invasion, unauthorized use or access, and other kinds of trespass. The secured object or perimeter may be, for example, a vehicle or a building. In addition to controlling alarm activation, engine starter, and engine computer, a typical security system designed for automotive applications often includes or controls various safety and convenience features, such as power door locks, power windows, and entertainment system installed in the vehicle.  
         [0003]     Many automotive security systems include a small hand-held remote control device, such as a key-fob, that allows the system&#39;s user to perform various operations remotely. For example, the remote control device may arm and disarm the security system, lock and unlock the doors and trunk, activate the siren, start the engine, and perform other functions when corresponding commands are entered by the user via the remote control device. If the security system is configured so that the remote control device can be used to unlock doors of an automobile without the capability to operate any other features, the system effectively becomes a keyless entry device.  
         [0004]     It is known in the art to automate the remote control function of a remote control device. For example, a hand-held remote control device may be configured to transmit periodically a command that unlocks doors and disarms the security system. The passive remote control command may be transmitted by the remote control device automatically. The command may also be transmitted in response to receipt by the remote control device of a “feeler” or interrogatory transmission that the base station periodically sends to the remote control device. Alternatively, the remote control device may send the initial interrogatory transmission to the base station, and transmit the passive remote control command after a “handshake” with the base station during which the base station verifies the identity of the remote control device. The doors would then automatically unlock and the system would disarm when the user carrying the hand-held device approaches the automobile. This feature, however implemented, is known as “passive” remote control. The system is passive in the sense that it unlocks doors and disarms itself without any deliberate user action, other than approaching the automobile.  
         [0005]     The time period between successive “unlock doors” and/or “disarm” command transmissions (i.e., “keyless entry” or “passive remote control” command transmissions) may vary widely. The period between these transmissions may be preset at the factory, or it may be user- or installer-configurable, and it may lie within broad time limits. But convenience considerations generally dictate that the transmissions take place often enough so that the doors would be unlocked by the time a user walking at a brisk pace approaches the automobile and attempts to open a door.  
         [0006]     Each transmission, including command and interrogatory transmissions, consumes electrical energy in addition to the energy consumed in the device&#39;s quiescent state between transmissions. The hand-held device is typically a portable device powered by a battery, for example, a primary or a secondary cell. Because the size of a typical hand-held device is small, the batteries used in such a device are also small, with rather limited energy storage capacity. To prolong battery life, it is desirable to limit the power dissipated by the hand-held device, including the power used for periodic interrogatory or command transmissions used for implementing passive remote control functionality. Reduction in transmitted power would also reduce the effective range of the passive remote control feature.  
         [0007]     There are other reasons to limit the effective range of the passive remote control feature, which apply regardless of whether the interrogatory transmissions are sent by the remote control device or the base station. Generally, it is desirable to unlock automobile doors automatically only when the user is in the immediate vicinity of the automobile, but not when the user is relatively far from the automobile. Automatically unlocking the doors and disarming the security system when the user cannot see the automobile leaves the automobile unprotected and accessible before the user can prevent unauthorized access. Even worse, accidental unlocking of the doors after the user has locked the doors and walked away may leave the automobile unprotected for a prolonged period. Moreover, a user may be annoyed by constant locking and unlocking of doors and arming and disarming of the security system when the automobile is parked in the driveway or garage of the user&#39;s home and the keychain with the hand-held device is stored in a safe place.  
         [0008]     To remedy this problem, a hand-held remote control device of one prior art system uses a movement sensor, such as a “shaker” element that includes a weight located by a spring so that acceleration of the sensor creates movement of the weight with respect to the body of the sensor. As long as the sensor detects that the remote control device is moving, the remote control device transmits the passive remote control command periodically, either automatically or in response to handshakes performed after the initial (interrogatory) transmissions. When the movement stops for a predetermined period of time, the transmissions also stop, saving power and preventing undesired unlocking/disarming events described above. Such solution, however, has a number of disadvantages.  
         [0009]     First, this approach necessitates inclusion of a movement sensor in the hand-held device, increasing both the cost and size of the device. Second, power savings are not realized when the user is continually moving. Third, the user may keep the hand-held device in a pocket while moving around the house, causing the undesirable locking and unlocking of doors, and arming and disarming of the security system. Therefore, it may still be desirable to limit the effective range of passive remote control command transmissions even in the systems where the remote control device includes a movement sensor.  
         [0010]     Another possible approach to the problems described above is to decrease the power transmitted by the hand-held device, so that the device functions only within a relatively close range of its base station. Unfortunately, a uniform reduction in the transmitted power of the hand-held device also limits the range of the non-passive transmissions, that is, transmissions initiated by the user&#39;s commands. The reduction also affects the reliability of active (i.e., non-passive) transmissions made from a short distance because of obstacles in the signal path, multi-path effects, and noise. For example, a “panic” alarm activation is preferably operative from the longest distance and with highest reliability achievable under cost, regulatory, and other system design constraints.  
         [0011]     A similar solution for systems where the interrogatory transmissions are periodically sent from the base station is to decrease the power sent by the base station. But a uniform reduction in the transmitted power would also adversely affect the range and reliability of transmissions other than the passive remote control transmissions. For example, low-power transmissions sent in response to an event at the base station, such as an alarm condition, might not be received by the remote control device under conditions that would allow the device to receive similar high-power transmissions.  
         [0012]     It would be advantageous to avoid the drawbacks of known systems while preserving transmission range and reliability of communications between the base station and the remote control device of a security system.  
       SUMMARY  
       [0013]     A need thus exists for reducing power consumption and transmission range of passive remote control commands issued by a remote control device, while preserving the transmission range of commands issued by the device in response to user inputs. A further need exists for reducing the range of base station interrogatory transmissions that enable passive operation of the security system, while preserving the range of other base station communications.  
         [0014]     Aspects of the present invention are directed to methods, apparatus, and articles of manufacture that satisfy one or more of these needs. In some aspects, the invention herein disclosed is a security system that includes a base station and a remote control device capable of transmitting one or more commands to the base station. The remote control device is configured (1) to transmit using a first power level a command of the one or more commands in response to user input, and (2) to transmit automatically using a second power level at least an initial portion of command of the one or more commands. The second power level is lower than the first power level.  
         [0015]     The one or more commands may include a plurality of active commands that are transmitted in response to user inputs. The one or more commands may include a command to unlock a door, disarm the security system, unlock the trunk, and/or start an engine, which command (or commands) may be transmitted both in response to user input and automatically as part of the passive remote control function of the system.  
         [0016]     In some aspects the second power level is between about ten decibels and about 16 decibels lower than the first power level. In a more specific aspect, the differential is about 10 decibels. Similarly, the second power level may be set so that the transmission range from the remote control device to the base station is limited to under about 75 feet. In a more specific aspect, the transmission range is limited to under about 20 feet. The first power level may be set within 3 decibels of maximum transmitted power legally allowed for transmissions such as transmissions of the commands from the remote control device in response to user input. The invention should not be understood as necessarily limited to any specific power level, power level differential, or transmission range.  
         [0017]     The remote control device may vary the second power level in response to changes in one or more operating parameters of the remote control device. The operating parameters affecting the second power level may include, for example, an indication of remaining life of the battery (e.g., battery voltage), movement of the remote control device, and time elapsed since a user of the device entered a command into the device.  
         [0018]     The specific dependence of the second power level on these and other operating parameters, and on other variables, may be programmed into the system by the system&#39;s user or installer. Programming of the first and second power levels may be performed, for example, through a programming port of the remote control device, or via a base station interface and the wireless communications link between the base station and the remote control device.  
         [0019]     Selected aspects of the invention are directed to a security system&#39;s base station and methods performed by the base station. In accordance with one aspect, a base station of a security system sends data to a remote control device of the security system using a first power level, and periodically sends an interrogatory transmission to the remote control device using a second power level. The second power level is lower than the first power level. When the interrogatory transmission is received by the remote control device, it triggers one or more responsive transmissions from the remote control device to the base station. The responsive transmissions may include a handshake between the remote control device and the base station. In the course of the handshake, the base station may send additional transmissions to the remote control device. In one aspect, base station&#39;s handshake transmissions to the remote control device are sent using the first power level.  
         [0020]     When the base station receives the one or more responsive transmissions, it verifies the identity of the remote control device from information in the one or more responsive transmissions, and executes at least one command. The base station may identify the command from information in the responsive transmissions. Exemplary commands include a command to unlock a door of a vehicle, disarm the security system of the vehicle, and start the vehicle&#39;s engine.  
         [0021]     One or both of the first and second power levels may be set when the base station receives the setting(s) from at least one of security system user and security system installer.  
         [0022]     Embodiments of the invention further include memories and other machine-readable articles of manufacture with program code embedded therein. The code, when executed by a processor of the remote control device or of the base station, configures the device or the station (as the case may be) to perform the methods described above.  
         [0023]     These and other features and aspects of the present invention will be better understood with reference to the following description, drawings, and appended claims.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0024]      FIG. 1  is a process flow diagram illustrating selected steps of a process for operating a multi-power mode remote control device of an automotive security system with passive remote control capability, in accordance with an embodiment of the present invention;  
         [0025]      FIG. 2  is a high-level block diagram of a security system, in accordance with an embodiment of the present invention;  
         [0026]      FIG. 3  is a high-level block diagram of the remote control of the security system of  FIG. 2 ;  
         [0027]      FIGS. 4, 5 , and  6  are process flow diagrams illustrating selected steps of processes for operating a multi-power mode remote control device with interrupt-driven processing of user-entered and automatic remote control commands, in accordance with an embodiment of the present invention.  
         [0028]      FIG. 7  is a process flow diagram illustrating selected steps of a process for operating a base station of an automotive security system with passive remote control capability and multi-power mode transmitter.  
     
    
     DETAILED DESCRIPTION  
       [0029]     In this document, including the appended claims, the words “embodiment” and “variant,” as well as similar expressions refer to particular apparatus or process, and not necessarily to the same apparatus or process. Thus, “one embodiment” or a similar expression used in one place or context can refer to a particular apparatus or process; the same or a similar expression in a different place can refer to a different apparatus or process. The expressions “alternatively,” “alternative embodiment,” and similar phrases are used to indicate one of a number of different possible embodiments. The number of potential embodiments is not necessarily limited to two or any other quantity. The words “couple,” “connect,” and similar expressions with their inflectional morphemes do not necessarily import an immediate or direct connection, but include connections through mediate elements within their meaning. “Operating parameters” or simply “parameters” refer to variable or variables that constitute the internal state of a remote control device and environmental factors affecting the remote control device. Other and further definitions and clarifications may be found elsewhere in this document. The definitions are intended to assist in understanding this disclosure and the appended claims, but the scope and spirit of the invention should not be construed as strictly limited to these definitions, or to the particular examples described in this specification.  
         [0030]     The invention herein disclosed can be implemented as part or feature of a security system such as systems described in the following patent documents:  
         [0031]     U.S. patent application entitled MENU-DRIVEN REMOTE CONTROL TRANSMITTER, filed on Oct. 30, 2003, application Ser. No. 10/699,009;  
         [0032]     U.S. provisional patent application entitled SECURITY AND REMOTE ACCESS FOR VEHICULAR ENTERTAINMENT, SAFETY, AND CONVENIENCE SYSTEMS, filed on Jan. 2, 2004, application Ser. No. 60/533,942; and  
         [0033]     U.S. patent Ser. No. 6,700,479.  
         [0034]     Each of these commonly-assigned applications and patent is incorporated by reference herein in its entirety, including all figures, tables, claims, and matter incorporated by reference therein.  
         [0035]     Reference will now be made in detail to several embodiments of the invention that are illustrated in the accompanying drawings. Same or similar reference numerals may be used in the drawings and the description to refer to the same or like apparatus elements and method steps. The drawings are in simplified form, not to scale, and omit apparatus elements and method steps that can be added to the described systems and methods, while including certain optional elements and steps.  
         [0036]      FIG. 1  is a process flow diagram illustrating selected steps and decision blocks of a process  100  for operating a multi-power mode remote control device of an automotive security system with passive remote control capability. Although certain process steps and decisions are described serially, some of these steps and decisions can be performed by separate elements in conjunction or in parallel, asynchronously or synchronously, in a pipelined manner, or otherwise. There is no particular requirement that the steps and decisions be performed in the same order in which this description lists them, except where explicitly so indicated, otherwise made clear from the context, or inherently required. Furthermore, not every illustrated step and decision is required in every embodiment in accordance with the invention, while some steps and decisions that have not been specifically illustrated may be desirable or necessary in some embodiments in accordance with the invention.  
         [0037]     At flow point  101 , the remote control device is ready to perform the steps of the process  100 . At step  105 , the remote control device checks (reads) an indicator that points out whether a user command has been received. The user may enter a command, for example, by pressing a key on the keypad of the remote control device. In performing the step  105 , the device may, for example, check a register that latches indications that a key has been pressed. At decision block  110 , the remote control device interprets the indicator to determine whether a command has indeed been entered by the user. If a command has not been entered, process flow proceeds to step  135 . Otherwise, process flow proceeds to decision block  115 .  
         [0038]     In general, the commands are of two kinds: (1) local, and (2) remote. A remote command requires communication with the vehicle-installed base station of the security system. A local command does not require such communication. In the decision block  115 , the remote control device determines whether the entered command is a local or a remote command. If the entered command is a local command, the remote control device performs the function or functions associated with the command, at step  120 , and returns to the step  105 . In the case of a remote command, the device configures its transmitter so that the transmitter will transmit at a relatively high power level. This is done in step  125 .  
         [0039]     As will be discussed in more detail below, the transmitter of the remote control device is capable of transmitting using two or more different power settings. For simplicity, two power level settings are discussed here: a high transmitted power level setting and a low transmitted power level setting. It should be noted that in the present context the “high” power level is high relative to the “low” power level, and vice versa. No specific absolute power level is implied by describing the power levels as either high or low. Thus, in the step  125  the transmitter is configured to transmit at a power level higher than at least one other power level at which the transmitter can transmit.  
         [0040]     At step  130 , the remote control device transmits to the base station the user command, or some information that has to be transmitted as part of performing the user command. At the same time, the remote control device may perform some other local operations associated with the command. Process flow then returns to the step  105 .  
         [0041]     Let us now return to the step  135 , to which the process  100  branches when the decision block  110  indicates that no user command has been entered. At this step, the remote control device checks (reads) its internal state to determine whether passive remote control functionality has been enabled and is currently appropriate. For example, the user or installer may be able to configure the remote control device so that passive remote control is either enabled or disabled. As part of the step  135 , the remote control device reads the programmed configuration variables affecting the passive remote control functionality.  
         [0042]     Furthermore, passive remote control may be selected for only a limited set of operating parameters. In this regard, the use of a movement (motion) sensor built into the remote control device has already been described above. Advantageously, the present invention may employ such sensor to enhance battery life. For example, the remote control device may be configured to enable passive remote control functionality only within a predetermined time period of movement indicated by the movement sensor. Similarly, the remote control device may be configured to disable the passive remote control functionality if no user command has been entered within a predetermined time period, for example, 24 hours. In one process embodiment, the passive remote control functionality is totally disabled after battery voltage or another indication of remaining battery life drops below a predetermined level. Alternatively, the time period of inactivity after which the remote control functionality is disabled is shortened in response to falling indication of remaining battery life. As a person skilled in the art would understand after perusal of this document, these techniques for selectively disabling or modifying passive remote control functionality are not exclusive; other techniques and combinations of techniques may be used for this purpose. Whatever the parameters controlling availability of the passive remote control functionality are, they are read in the step  135 .  
         [0043]     At decision block  140 , the remote control device determines, based on the parameters read in the step  135 , whether the passive remote control functionality is enabled, and, therefore, whether passive transmissions of the remote control commands should be performed. If the parameters indicate that the transmissions should not be performed, process flow returns to the step  105 . If the parameters indicate that the transmissions should be performed, process flow advances to step  145  to read the value of a passive remote control transmission timer.  
         [0044]     At decision block  150 , the remote control device determines whether the transmission timer has expired. If the timer has not expired, process flow returns once again to the step  105 . If the timer has expired, indicating that a passive remote control command should be sent, process flow continues with step  155 , in which the transmitter is configured to transmit at a relatively low power level. Again, the power setting is “low” in comparison to the “high” transmitter power setting of the step  125 .  
         [0045]     At step  160 , the remote control device transmits a passive remote control command. In some embodiments, the command is a simple security system disarm directive. In other embodiments, the security system disarm directive is combined with another instruction, for example, a door unlock command or a command to start engine. Still other commands may be sent in other embodiments consistent with the invention.  
         [0046]     At step  165 , the remote control device resets the passive remote control transmission timer, so that the countdown to the next passive transmission begins anew. Process flow then returns to the step  105 .  
         [0047]     It should be noted that in the above description of the process  100 , as well as throughout this document, including the appended claims, transmitting a command does not necessarily imply a single transmission. In some embodiments, the remote control device sends an interrogatory transmission and then listens for a response from the base station. If the base station receives the interrogatory transmission and recognizes a code embedded therein, it sends back a responsive handshake message acknowledging the receipt and authenticating the base station. The remote control device receives the response and then sends the appropriate instruction or other information, for example, a passive remote control instruction. The initial transmission may be active, i.e., user-initiated, or passive, i.e., made automatically and not in response to user input. In the context of the present document, a “command” sent by a remote control device refers to the interrogatory transmission, transmissions made in the course of the handshake process, and the actual instruction/directive that specifies the function to be performed by the base station. In embodiments where handshake is not implemented and interrogatory transmissions are not used, the word “command” refers to the actual instruction sent from the remote control device to the base station. The remote control device uses the low power level to make periodic transmissions to the base stations, for example, the interrogatory transmissions. Following the initial interrogatory transmission, the transmitter power level may be increased for transmission of the handshake and of the actual instruction.  
         [0048]      FIG. 2  is a simplified schematic diagram of a vehicle security system  200  that can perform the steps of the processes described in this document. As illustrated, the system incorporates a remote control device  290 , wireless link  260 , and base station  205  that includes the remaining components shown in  FIG. 2  (appearing within the dotted lines). The remote control device  290  includes a variable output power transceiver  311 , antenna  312 , and processor subsystem (e.g., a controller)  331 .  
         [0049]     The base station  205  includes a base controller  230 ; a base transceiver  210  with its antenna  211 ; sensors  215 ,  217 , and  219 ; and various additional inputs and outputs. The base controller  230  includes a processing unit  201 , a non-volatile instruction memory  202 , and operation memory  203 . In the described embodiment, the base controller  230  is implemented as a microprocessor  201  with internal memory modules  202  (ROM) and  203  (RAM). As illustrated in  FIG. 2 , an external non-volatile memory device  204 , such as an electrically erasable programmable read-only memory (EEPROM), can supplement the microprocessor memory, storing, for example, field-configurable control data and remote controller recognition codes.  
         [0050]     The code of the program executed by the base controller  230  is normally embedded at the factory during the integrated circuit manufacturing process, but it can also be loaded or burned-in from a variety of sources in the field, for example, from a programming tool, machine-readable medium, such as a CD, DVD, flash memory, semiconductor ROM device, floppy or hard drive, or a similar memory or storage device. The code may also be loaded via a network, such as the Internet.  
         [0051]     The base transceiver  210  communicates with the remote control device  290  over the link  260 . Thus, the base controller  230 , which is coupled to the transceiver  210  through interface line(s)  213 , can communicate with the remote control device  290  through the base transceiver  210  and the link  260 .  
         [0052]     In the illustrated embodiment, the transceiver  210  includes a transmitter section  210   a  capable of transmitting commands and other data to the remote control device  290 , a receiver section  210   b  capable of receiving data from the remote control device  290 , and a power control section  210   c  that controls the power output level of the transmitter section  210   a . The base controller  230  configures the power control section  210   c  through the interface line(s)  213 .  
         [0053]     In some embodiments, the transceiver  210  has a variable power transmitter capable of transmitting using two or more different power levels. One or more of the power levels may be user- or installer-configurable. In an embodiment, the transceiver  210  includes an AWICS-09325 IC-based RF Transceiver Module.  
         [0054]     Although in the described embodiment the link  260  is shown as a bi-directional link, in some alternative embodiments the link  260  is unidirectional, carrying commands from the remote control device  290  to the base controller  230 , but not in the opposite direction; in such embodiments, a simple receiver can perform the necessary functions in place of the transceiver  210 .  
         [0055]     The sensors of the described device  205  include a shock sensor  215 , a field disturbance sensor  217 , and a glass break sensor  219 . Any other sensors appropriate to an automotive security system (or another installed environment) can be included as well.  
         [0056]     Among the additional inputs to the base station  205  are these: +/− door inputs  228  and  227 ; a light sensor input  243 ; a valet/program control switch input  222 ; an ignition input  221 ; and a program lockout input  242 , intended to prevent both accidental and intentional (subversive) programming of the base station  205 , and programming of the remote control device  290  through the base station  205 .  
         [0057]     Lines  231  through  236  provide the following signal and control outputs:  
         [0058]     Power door lock and unlock outputs— 231 ;  
         [0059]     Ground when armed and ground when armed-plus-ignition outputs for starter interrupt— 232 ;  
         [0060]     LED indicator outputs— 233 ;  
         [0061]     Speech, horn, and siren outputs for audible alarms and warnings— 234 ;  
         [0062]     Headlights, running lights, and dome light outputs— 235 ; and  
         [0063]     Channels 2 (trunk), 3, 4, 5, and 6 auxiliary outputs— 236 .  
         [0064]     In a variant of the remote control system embodiment illustrated in  FIG. 2 , the base station includes remote start capability that uses additional inputs and outputs to enable the base station to start the vehicle. In this variant, the base station  205  further includes tachometer, neutral sense, brake activation, hood position, and remote starter activation outputs. Some of the added outputs are as follows: starter output; ignition output(s); and accessory output(s) for controlling the heater, air conditioner or other vehicle functions.  
         [0065]      FIG. 3  illustrates a simplified block diagram of an embodiment of the remote control device  290  built on the platform of a controller  331 , which can be, for example, a microcontroller (MCU), a microprocessor, or an application-specific integrated circuit. In the specific embodiment of  FIG. 3 , the controller  331  is a microcontroller. It includes a processing unit  301 ; random access memory  306  for use as operating registers, address registers, and for other data storage during program execution; and memory modules  303  and  305  for storing program instructions and data. The memory modules  303  and  305  can be, for example, read only memories (ROMs), programmable ROMs (PROMs), electrically programmable ROMs (EPROMs), and electrically erasable PROMs (EEPROMS). The memory module  305  is typically used to store program instructions and constants. In the embodiment of  FIG. 3 , the memory module  303  is a non-volatile, re-writable memory module, such as Flash, EEPROM, or low-power battery-backed memory. It is used to store programmable control and configuration data, such as transmitter identification code, icon definitions, and menu lists for the functional and operational routines of the remote control device  290 .  
         [0066]     The code of the program executed by the controller  331  is normally embedded at the factory during the integrated circuit manufacturing process, but it can also be loaded or burned-in from a variety of sources in the field, for example, from a programming tool, machine-readable medium, such as a CD, DVD, flash memory, semiconductor ROM device, floppy or hard drive, or a similar memory or storage device. The code may also be loaded via a network, such as the Internet.  
         [0067]     Numeral  395  designates a port through which the remote control device  290  can receive its operating software and configuration parameters. In the embodiment of  FIG. 3 , the port  395  is a custom serial data port. In other embodiments, the port can be implemented, for example, as a Universal Serial Bus (USB); an RS  232  serial port; a parallel port; as a wired or wireless (e.g., IR, RF, ultrasound) network connection to a WAN (e.g., the Internet), LAN, intranet, or extranet; as a memory storage reader device; or as a receiver, transceiver, modem, or another communication interface device.  
         [0068]     The controller  331  also has an input-output (I/O) section that provides the controller  331  with capability to read inputs and drive outputs under program control. The inputs of the I/O section of the controller  331  include connections to user-operable inputs  323  and  324 , such as a scroll switch, a selection switch, and a keypad. The outputs of the I/O section further include the outputs  314  for driving a display  350 ; transceiver input/output lines  313  used to send data to and receive data from the base station  205  via the transceiver  311 ; and control interface lines  315  used to set the power level of the transmissions made by the transceiver  311 . The control lines  315  may include a serial peripheral (SPI) interface. SPI is a synchronous serial data link that is standard across many Motorola microprocessors and other peripheral chips.  
         [0069]     The display  350  is part of the user interface of the remote control device  290 . It can be a graphical or an alphanumeric display.  
         [0070]     The transceiver  311  can accept data for transmission to the transceiver  210  of  FIG. 2 . As mentioned previously, the link  260 , over which the transmitter  290  and the transceiver  210  communicate, can be an RF, IR, ultrasound, or another kind of link. The nature of the link  260  dictates the specifics of the transceiver  311  and the transceiver  210 . In an embodiment, the transceiver  311  includes an AWICS-09325 IC-based RF Transceiver Module.  
         [0071]     The transceiver  311  includes a transmitter section  311   a  capable of transmitting commands and other data to the base station  205 , a receiver section  311   b  capable of receiving data from the base station  205 , and a power control section  311   c  that controls the power output level of the transmitter section  311   a . The controller  331  configures the power control section  311   c  through one or more control interface lines  315 . In some embodiments, the control interface lines  315  may be combined with the lines  313  as part of a single interface.  
         [0072]     Two different transmitter power settings can be selected by the controller  331 . In one embodiment, the high power level approaches (within 3 dB) the maximum transmitted power level allowed by rules of the Federal Communication Commission applicable to remote control devices of automotive security systems, while the low power level is such that the range of the remote control device  290  does not exceed about 75 feet (22.5 meters). In another embodiment, the low power level is set so that the range of the remote control device  290  does not exceed about 20 feet (6 meters). In yet another embodiment, the difference between the low power level and the high power level is about 10 decibels (dB). In still other embodiments, the difference between the low power level and the high power level is between about 10 dB and 16 dB. The broad concepts of the invention should not be construed as limited to any of these distances or decibel values. Furthermore, three or more transmitter power settings may be available in some embodiments.  
         [0073]     It should be noted that the divisions between the sections  311   a ,  311   b , and  311   c  are shown for illustration; the demarcation lines between these sections are quite arbitrary. Moreover, the power control section may also perform other control functions within the transceiver  311 , and may be tightly coupled to both the transmitter section  311   a  and the receiver section  311   b . In some embodiments, the control of transmitted power is achieved through reduction of power supplied to the transmitter section  311   a . Two or more transmitter power settings are available for selection by the controller  331 . In various embodiments, one or more of these power levels may be user- or installer-configurable within predetermined limits. For example, the low power level may be allowed to vary within broad limits to accommodate the user&#39;s specific preference of balance between battery conservation and range of passive remote control command transmissions.  
         [0074]     The process  100  is of course exemplary and not uniquely required for practice of the invention, as is the case with other process and apparatus embodiments described in this document. Many other variations on the multi-power mode transmission technique will surely occur to a person skilled in the art after perusal of this document. To illustrate, an additional embodiment of a multi-power mode remote control device is described below.  
         [0075]      FIGS. 4, 5 , and  6  are process flow diagrams illustrating selected steps and decision blocks of processes  400 ,  500 , and  600  for operating a multi-power mode remote control device with interrupt-driven processing of user-entered and passive remote control commands. Although certain process steps and decisions are described serially, some of these steps and decisions can be performed by separate elements in conjunction or in parallel, asynchronously or synchronously, in a pipelined manner, or otherwise. There is no particular requirement that the steps and decisions be performed in the same order in which this description lists them, except where explicitly so indicated, otherwise made clear from the context, or inherently required. Furthermore, not every illustrated step and decision is required in every embodiment in accordance with the invention, while some steps and decisions that have not been specifically illustrated may be desirable or necessary in some embodiments in accordance with the invention.  
         [0076]     The process  400  is an interrupt-driven (interrupt-initiated) process for sending a user-entered command, i.e., an active command. It begins at flow point  401  with the remote control device being previously initialized and ready for operation. At step  405 , the controller of the remote control device receives an interrupt from the user interface of the remote control device, such as the user-operable inputs  323 / 324 . At step  410 , the device identifies the specific command entered by the user. At decision block  415 , the remote control device determines whether the command is a local command. If the command is a local command, process flow proceeds to step  420  to perform the local command. After the step  420 , the process  400  terminates at flow point  402 .  
         [0077]     If the remote control device determines, at the decision block  415 , that the entered command is not a local command, i.e., it is a remote command, process flow branches to step is  421  to read and store the state of the passive remote control transmit timer interrupt (masked or unmasked). At step  422 , the passive remote control transmit timer interrupt is masked. The passive remote control transmit timer interrupt results from expiration of the passive remote control transmit timer, which is analogous to the similarly named timer previously described in relation to  FIG. 1 . The reason for masking the passive remote control transmit timer interrupt is to prevent passive (automatic) transmissions to the base from disrupting or delaying transmissions due to user commands.  
         [0078]     At step  425 , the remote control device configures its transmitter so that the transmitter will transmit at a relatively high power level.  
         [0079]     At step  430 , the remote control device transmits to the base station the user command, or some information that has to be transmitted as part of performing the user command.  
         [0080]     At decision block  431 , the device determines whether the passive remote control transmit timer interrupt was masked before the step  422 . If the interrupt was masked, process flow terminates at the flow point  402 . Otherwise, the device unmasks the interrupt at step  432  to enable automatic transmissions to the base station. Process flow then terminates at the flow point  402 .  
         [0081]     The process  500  may be performed in response to a change in any of the operating parameters of the remote control device. Recall that the parameters may change, for example, when the device is being moved, when the movement ceases, or when the battery voltage falls below a predetermined threshold. Beginning with flow point  501 , the process flow proceeds to step  535  to read the parameters. At decision block  540 , the remote control device determines, based on the parameters read in the step  535 , whether the passive remote control functionality is enabled, and, therefore, whether automatic transmissions of the passive remote control commands should be performed. If the parameters indicate that the transmissions should be performed, process flow advances to step  541  to determine an appropriate setting for the passive remote control transmit timer. Recall that this setting may be a function of the operating parameters. At step  542 , the device sets the timer in accordance with the determination of the step  541 , and, at step  543 , unmasks the passive remote control transmission interrupt. After the interrupt is unmasked, process flow terminates at the flow point  502 .  
         [0082]     If the determination made at the decision block  540  indicates that passive remote control functionality should be disabled, the remote control device proceeds to step  544  to mask the passive remote control transmit timer interrupt. Process flow then terminates at the flow point  502 .  
         [0083]     The process  600 , which sends the automatic (passive) remote control commands, begins at flow point  601 . At step  652 , the remote control device receives the passive remote control transmit timer interrupt occasioned by expiration of the passive remote control transmit timer. At step  655 , the device configures the transmitter to transmit at a relatively low power level. At step  660 , the device transmits the passive remote control command at the low power level. The process  600  then terminates at flow point  602 .  
         [0084]     Turning now to an embodiment in which the base station sends interrogatory transmissions,  FIG. 7  is a process flow diagram illustrating selected steps and decision blocks of a process  700  for operating a base station of an automotive security system with passive remote control capability and multi-power mode transmitter. Although certain process steps and decisions are described serially, some of these steps and decisions can be performed by separate elements in conjunction or in parallel, asynchronously or synchronously, in a pipelined manner, or otherwise. There is no particular requirement that the steps and decisions be performed in the same order in which this description lists them, except where explicitly so indicated, otherwise made clear from the context, or inherently required. Furthermore, not every illustrated step and decision is required in every embodiment in accordance with the invention, while some steps and decisions that have not been specifically illustrated may be desirable or necessary in some embodiments in accordance with the invention.  
         [0085]     At flow point  701 , the base station is initialized and ready to communicate with the remote control device.  
         [0086]     At step  705 , the base station checks its internal state to identify any pending remote communication requests. For example, the base station may (1) read registers that latch newly-originated alarm conditions (e.g., zone violations) and other externally-driven events, (2) read the passive remote control transmit timer that controls periodic interrogatory transmissions, and (3) read registers that contain other pending transmissions to be sent to the remote control device, such as handshake transmissions.  
         [0087]     At decision block  710 , the base station determines whether a remote communication request is pending. If there are no current remote communication requests, process flow returns to the step  705 . Otherwise, the base station determines, at decision block  715 , whether the pending communication request that is being processed corresponds to an interrogatory transmission used for passive remote control.  
         [0088]     If the pending remote communication request corresponds to an interrogatory transmission used for passive remote control, the base station advances from the decision block  715  to step  755  to configure the base station transmitter to transmit at a relatively low power level.  
         [0089]     Note that the transmitter of the base station is capable of transmitting using two or more different power level settings, as was the case with the transmitter of the remote control device used to perform the process  100  discussed above. For simplicity, two power level settings are discussed here: a high transmitted power level setting and a low transmitted power level setting. The “high” power level is high relative to the “low” power level, and vice versa. No specific absolute power level is implied by describing the power levels as either high or low.  
         [0090]     After the transmitter is configured for low power transmissions, the base station sends the interrogatory transmission. Process flow then returns to the step  705  at the beginning of the process  700 .  
         [0091]     If the pending remote communication request does not correspond to a passive remote control interrogatory transmission, as determined in the decision block  715 , the base station proceeds to step  725 . Here, the base station configures its transmitter to transmit at a relatively high power level, i.e., at a power level higher than that of step  755 . After the transmitter is configured for high power transmissions, the base station sends the transmission corresponding to the pending remote communication request, at step  730 . Process flow then returns once again to the step  705 .  
         [0092]     In operation, the base station continually examines its internal state to determine whether remote communication requests are pending. A pending remote communication request is a need to send a transmission from the base station. If the pending request is a request to send an interrogatory transmission to the remote control device for the purpose of enabling passive remote control, the base station configures its transmitter to transmit at a relatively low power level. For at least some other remote communication requests, the base station configures the transmitter to transmit at a relatively high power level. The base station then transmits using the selected power level. Thus, the effective range of the interrogatory transmissions is shorter than the effective range of other transmissions, for example, transmissions communicating alarm conditions to the remote control device of the security system.  
         [0093]     In some embodiments the second power level is between about ten decibels and about sixteen decibels lower than the first power level. In a more specific embodiment, the differential is about 10 decibels. Similarly, the second power level may be set so that the transmission range from the base station to the remote control device is limited to under about 75 feet. In a more specific embodiment, the transmission range is limited to under about 20 feet. The first power level may be set within 3 decibels of maximum transmitted power legally allowed for transmissions such as transmissions from the base station to the remote control device. The invention should not be understood as necessarily limited to any specific power level, power level differential, or transmission range.  
         [0094]     In some embodiments, the system remote control device can be configured to recognize a reading of a signal strength indicator (SSI) as an indication of the distance from the base station. Likewise, the system base station can be configured to recognize an SSI reading as an indication of the distance from the remote control device and to disarm or not disarm the system based on the SSI level when the system is in the passive recognition mode. Even if both the base station and the remote control device have multi-power levels and the power level indicator is embedded and transmitted in the code word, each unit can be configured to recognize the SSI level as an indication of distance from the other device.  
         [0095]     This document describes the inventive apparatus, methods, and articles of manufacture enabling multi-power mode functionality in considerable detail. This was done for illustration purposes only. Neither the specific embodiments of the invention as a whole, nor those of its features limit the general principles underlying the invention. The specific features described herein may be used in some embodiments, but not in others, without departure from the spirit and scope of the invention as set forth. Various physical arrangements of components and various step sequences also fall within the intended scope of the invention. Furthermore, the invention need not be limited to automotive or vehicular applications, but may extend to applications involving other kinds of security and convenience systems, and beyond. Many additional modifications are intended in the foregoing disclosure, and it will be appreciated by those of ordinary skill in the art that in some instances some features of the invention will be employed in the absence of a corresponding use of other features. The illustrative examples therefore do not define the metes and bounds of the invention and the legal protection afforded the invention, which function is carried out by the claims and their equivalents.