Abstract:
Building monitoring and control systems including bi-directional radio frequency links between master and remote units wherein the remote units operate in a low power, non-receiving state a majority of the time is disclosed. The bi-directional capability allows coordinated scheduling which aids in allowing the remote units to transmit data only at periodic time intervals to extend battery life. The bi-directional capabilities also allow for re-read requests for alarm validation and for putting remote units in armed and disarmed states for power conservation.

Description:
This application is a continuation of U.S. application Ser. No. 09/311,092 filed May 13, 1999. 

   CROSS REFERENCE TO CO-PENDING APPLICATIONS 
   The present application is related to U.S. patent application Ser. No. 09/311,242 filed May 13, 1999, entitled “Output Buffer With Independently Controllable Current Mirror Legs”; U.S. patent application Ser. No. 09/311,105, filed May 13, 1999, entitled “Differential Filter with Gyrator”; U.S. patent application Ser. No. 09/311,234, filed May 13, 1999, entitled “Compensation Mechanism For Compensating Bias Levels Of An Operation Circuit In Response To Supply Voltage Changes”; U.S. patent application Ser. No. 09/311,246, filed May 13, 1999, entitled “Filter With Controlled Offsets For Active Filter Selectivity and DC Offset Control”; U.S. patent application Ser. No. 09/311,250, filed May 13, 1999, entitled “Wireless System With Variable Learned-In Transmit Power”; and U.S. patent application Ser. No. 09/311,014, filed May 13, 1999, entitled “Wireless Control Network With Scheduled Time Slots”, all of which are assigned to the assignee of the present invention and incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates generally to building monitoring and control for commercial and residential use. More specifically, the present invention relates to building monitoring and control systems such as security, HVAC or other monitoring systems that utilize wireless, bi-directional radio frequency communication between master units and remote units. In particular, the present invention relates to remote units having low transmission duty cycles, low power consumption, and alarm validation capabilities. 
   BACKGROUND OF THE INVENTION 
   Building monitoring and control systems including security system, HVAC and other monitoring and control systems are in increasing use in both commercial buildings and residential dwellings. For security systems, the increasing use is due in part to a long-term perception of increasing crime rates along with increasing awareness of the availability of building monitoring and security systems. For HVAC systems, the increasing use is due in part to the desire to reduce heating and cooling costs, and to save energy. 
   A building monitoring and/or control system typically includes a variety of remote units coupled to detection devices and at least one master unit which typically resides in a central location in the building and can include annunciation functions and reporting functions to another location such as a central reporting service or police department. Remote units have, in the past, been hard wired to the master unit. For example, in a security system, reed switches or Hall effect switches are often disposed near magnets located near doors and door jambs, with a door opening making or disrupting continuity, with the resulting signal being received by the master unit. 
   In hardwired systems the remote units and the detection devices may be nearly one in the same. For example, the detection device may be a foil trace on a glass pane and the remote unit may be wire terminals with optional signal conditioning equipment leading to a wire pair connected to the master unit. Hard wired units can be installed most easily in new construction, where running wire pairs is easier than in existing buildings. Installing hard-wired systems can be very expensive in existing buildings due in part to the labor costs of snaking wires through existing walls and ceilings. In particular, on a point-by-point basis, retrofitting residential dwellings can be expensive because houses are often not designed to be continually changed, as are many office buildings. For example, most houses do not have dropped ceilings and utility closets at regular intervals. Houses can have higher aesthetic expectations than commercial office buildings, requiring greater care in installing and concealing wiring. 
   Wireless security systems have become increasingly common. Existing systems use radio frequency transmission, often in the 400 MHz region. Wireless systems can greatly reduce the need for wiring between remote and master unit or units. In particular, wireless systems can communicate between the remote units and the master units without wiring. Remote units still require power to operate, and can require wiring to supply that power, which can add a requirement for power wiring where the power had been provided in hard wired systems over the wiring used to communicate between remote units and the master unit. The power requirement can partially negate the wireless advantage of radio frequency units, as some wiring is still required. The power supply wiring requirement is often eliminated with the use of batteries. Battery life is largely a function of power consumption of the remote units. The power consumption is dependent upon both the electronics and upon the duty cycle of the unit. 
   Current wireless systems typically utilize remote units which can only transmit and master units which only receive. Remote units often transmit sensor data for needlessly long periods, and at higher power than is required, as there is no bi-directional capability, and therefore no way for the master unit to acknowledge receipt of the first remote unit message, or a low power message. Sometimes, the remote units transmit a health status message at regular periodic intervals. The health status message gives the health of the remote unit, sometimes includes sensor data, and informs the master unit that the remote unit is still functioning. The periodic transmissions can be scheduled at the remote units by DIP switches or local programming of the remote units, but typically cannot be adjusted by the master unit as the communication between master and remote is unidirectional and the master has no way to adjust the timing of transmissions of the remote units. Since there is no coordination between the transmission times of the remote units, collisions can occur between remote unit transmissions, which may reduce the overall reliability of the system. To increase the probability that a particular remote unit transmission is received by the master, the remote unit may make the same transmission many times. However, this can significantly increase the power consumed by the remote units. 
   Another limitation is that false alarms can be generated. False alarms undermine the credibility of real alarms and can cost money to respond to. For security systems, private security firms often charge to investigate alarms reported to them. Many municipalities charge large fees for false alarms that are reported to police departments. Too many false alarms can result in all or part of a security system to be ignored or turned off entirely. For HVAC systems, false alarms can cause, for example, heat to be applied even if it is not desired. As can be seen, this can decrease the efficiency of the HVAC system. 
   What would be desirable, therefore, is a bi-directional wireless security, HVAC or other building monitoring system that allows communication between the master and remote units for increased reliability. What would also be desirable is a system that has one or more low power modes for conserving valuable power resources. 
   SUMMARY OF THE INVENTION 
   The present invention includes a building monitoring and/or control system that includes bi-directional radio frequency links between master and remote units wherein the remote units preferably operate in a low power, non-transceiving state a majority of the time. The system can include at least one master unit and a plurality of remote units, the remote units being typically coupled to sensors for measuring and/or controlling security or building environment variables. The remote units in most systems can operate in a low power consumption state in which the unit can neither transmit nor receive, in a receive state in which the unit consumes more power and can receive transmissions from the master unit, and in a transmit state in which the unit consumes more power and can transmit messages to the master unit. Some embodiments include armed states in which the remote unit can sense and transmit data, and disarmed states in which the remote unit cannot, in combination, sense and transmit data. Disarmed states can provide a low power consumption state in which power is consumed neither for sensing variables nor for transmitting data. 
   In some embodiments, remote units are in a receive state only for a period after transmitting. In some embodiments, the remote units are in a receive state only after transmitting and are in a receive state periodically, often waiting for polling by a master unit. Some remote units transmit data at periodic intervals and transmit data after the occurrence of an event. Events can include timeout events, sensor change events, and polling events. In preferred embodiments, remote units await acknowledgment from a master unit after a transmission. After receipt of an acknowledgment, the remote units preferably do not further transmit the same message. 
   Remote unit sensors can be used to detect state changes in security devices such as door and window switches. Sensors can also be used to measure analog or continuously variable properties of a building environment such as temperature, humidity, airflow, and hot water flow. In some embodiments, upon expiration of a timer, building data such as temperature is reported as an event in the same manner as a door opening. 
   In one process suitable for executing in a remote unit, the remote unit: determines a time for communication with a master; waits in a low power non-receive and non-transmit state for either a timeout to arrive or an event to occur; changes to a transmitting state upon detecting the event and transmits data to the master unit; changes to a transmitting state upon occurrence of the timeout and transmits data to the master unit; waits for acknowledgement from the master unit after transmitting data; and resumes the low power state. If acknowledgement is not received, in preferred embodiments, retransmission is performed, perhaps at a higher power level. In one process, timing information for the next transmission is received by the remote unit along with the acknowledgment. The acknowledgement can be used to re-synchronize the timer of the remote unit with the timer of the master unit. In one process, frequency information relating to the next transmission is received by the remote unit along with the acknowledgment. 
   In one system, remote units have an armed state in which the sensors can sense and the unit can transmit and a disarmed state in which, in combination, the sensors cannot both sense and the remote unit transmit. In the disarmed state, the sensor cannot sense and/or the transmitter cannot transmit. In the previously described disarmed state, in some embodiments, the sensor functionality is disabled to save energy. In some embodiments, the transmitting functionality is disabled to prevent transmissions even when otherwise transmittable events occur. For example, in a disarmed state, a door reed switch may still sense continuity, but the door opening will not be transmitted, to save on energy and extend battery life when the door opening is not a concern. In some embodiments, both sensor and transmitting functionality are disabled to save on energy and extend battery life. It is contemplated that the sensor state may be reconfigured on the fly depending on the current mode of the system. 
   In some systems, the master unit, upon receiving an event from a remote unit, can request a re-read of the sensor to validate the event before taking further action. A decision whether to request a re-read can be based on the sensor type and the current mode of the system. In one embodiment, the sensor type is transmitted along with the data. The sensor type is determined in another embodiment by the master looking up the remote unit ID and determining the sensor type or types associated with it. The sensor type is determined in another embodiment by the master looking up the sensor type in a previously built table. The table can be built from data obtained at initialization of either the remote units or the master unit. The information associated with a remote unit sensor can include whether to re-read, how long to wait before a re-read, and how many times to re-read. The validation functionality can greatly reduce false alarms. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a wireless control system having a master unit and two remote units; 
       FIG. 2  is a block diagram of a wireless remote unit having a transceiver coupled to a controller; 
       FIG. 3  is a block diagram of a master unit having a transceiver coupled to a controller; 
       FIG. 4  is a state transition diagram of a process which can execute in a remote unit; 
       FIG. 5  is a state-transition diagram of a process which can execute in a remote unit for arming and disarming a remote device; and 
       FIG. 6  is a state-transition diagram of a process which can execute in a remote unit for handling confirmation requests by a master unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a wireless control system  20  including a master unit  22  and two wireless remote units  24  and  25 . Master unit  22  includes an antenna  26 , a power supply line  28 , annunciator panel output line  30 , alarm device output line  32 , and telephone line  34 . A building monitoring and/or control system according to the present invention typically has at least one master unit which is commonly powered with AC line power but can be battery powered, or have battery back-up power. Remote unit  24  includes an antenna  23  and is coupled to two discrete sensor inputs  36  and  38 . Sensor input  36  is a normally open sensor and sensor input  38  is a normally closed sensor. Sensors  36  and  38  can be reed switches or Hall effect devices coupled to magnets used to sense door and window opening and closing. Sensor  38  can be a foil continuity sensor used to detect glass breakage. Remote unit  25  includes antenna  23  and two analog sensors  40  and  42 . Sensor  40  is a variable resistance device and security sensor  42  is a variable voltage device. Analog sensors can measure variables such as vibration, noise, temperature, movement, and pressure. Sensors typically sense or measure variables and output data. The data can be binary or discrete, meaning on/off. Data can also be continuous or analog, meaning having a range of values. Analog data can be converted to digital form by using an A/D converter. 
   Examples of sensors include intrusion sensors such as door switches, window switches, glass breakage detectors, and motion detectors. Safety sensors such as smoke detectors, carbon monoxide detectors, and carbon dioxide detectors are also examples of sensors suitable for use with the current invention. Other sensors include temperature sensors, water detectors, humidity sensors, light sensors, damper position sensors, valve position sensors, electrical contacts, BTU totalizer sensors, and water, air and steam pressure sensors. In addition to sensors, output devices can also be included with the present invention. Examples of output devices include valve actuators, damper actuators, blind positioners, heating controls, and sprinkler head controls. In one embodiment, remote devices having output capabilitity utilize circuitry identical or similar to the circuitry used for sensors, particularly for the communication and controller portions of the devices. Remote devices coupled to output devices typically are hard wired to power sources as they typically consume more power than the sensor input devices. For this reason, remote devices having output devices may not benefit as much from the power saving features of the present invention. 
   A building monitoring and/or control system according to the present invention can have a large number of remote units which can be spread over an area covered by the RF communication. One system can have remotes located about 5,000 feet (of free space) away from the master unit. The actual distance may be less due to intervening walls, floors and electromagnetic interference in general. Systems can have repeater units as well, units that receive and re-transmit messages to increase the area covered. In some systems, repeaters have a receiver coupled to a transmitter by a long, hard-wired link, allowing separate areas to be covered by one master unit. 
   Referring now to  FIG. 2 , a remote unit  50  is illustrated in further detail, including antenna  23 , a transceiver  52 , and a controller  54 . Transceiver  52  and controller  54  are each coupled to power source  56  in the embodiment illustrated. Controller  54  includes a programmable microprocessor such as the PIC microprocessor in one embodiment. In another embodiment, the controller is formed primarily of a once-programmable or writeable state machine. Transceiver  52  is preferably a UHF transceiver, for example transmitting and receiving in the 400 or 900 MHz range. Transceiver  52 , in one embodiment, can be set to transmit and receive on different frequencies and to rapidly switch between frequencies. While transceiver  52  can include the capability to transmit and receive simultaneously, in a preferred embodiment, transceiver  52  can only either receive or transmit, but not both at the same time. In the embodiment illustrated, controller  54  is coupled to transceiver  52  with control input line  58 , control output line  60 , serial input line  62 , and serial output line  64 . 
   Control input line  58  can be used to reset the transceiver, to set modes, and to set transmit and receive frequencies. Control output line  60  can be used by signal controller  54  to determine when communication receptions or transmissions have been completed. Serial input line  62  can be used to feed messages to be transmitted to transceiver  52  as well as frequencies to be used and other control parameters. Serial output line  64  can be used to provide messages received from transceiver  52  to controller  54  and can be used to convey information about signal strength to controller  54 . The controller and serial lines can of course be used for any purpose and the uses discussed are only a few examples of such uses in one embodiment. In some embodiments, the serial lines are used to convey both status and control data. 
   Remote unit  50  can also include sensor input lines  66  for coupling to security sensors and other devices. A reset line  68  can be coupled to a reset button to reset remote unit  50  when re-initialization of the unit is desired, such as at the time of installation or after battery changes. In some embodiments, battery power resumption serves as the reset function. A power line  56  is illustrated supplying both transceiver  52  and controller  54 . In some embodiments, power is supplied directly to only the controller portion or the transceiver portion, with the controller portion supplied from the transceiver portion or visa versa. In the embodiment illustrated, controller  54  and transceiver  52  are shown separately for purposes of illustrating the present invention. In one embodiment, both controller  54  and transceiver  52  are included on the same chip, with a portion of the gates on board the chip dedicated for use as controller logic in general or used as a user programmable microprocessor in particular. In one embodiment, a PIC microprocessor is implemented on the same chip as the transceiver using CMOS logic and the PIC microprocessor is user programmable in an interpreted BASIC or JAVA language. 
   Referring now to  FIG. 3 , master unit  22  is illustrated, including a transceiver portion  70  and a controller portion  72 . Master unit  22  includes control lines  74  and  76  and serial lines  78  and  80 . Reset line  82  is included in the embodiment illustrated as is a programmable input line  86 , a panel LED output line  84 , horn output line  32  and telephone line  34 . Programmable input line  86  can be used for many purposes, including down loading control logic, inputting keyboard strokes, and inputting lines of BASIC or JAVA code to be interpreted and executed. Panel LED line  84  can be used to control panel-mounted LEDs giving status information. Horn line  32  can be used to activate alarm horns or lights. Telephone line  34  can be used for automatic dial out purposes to report security breaches to a reporting service or to the police. 
   In one embodiment, master unit  22  and remote unit  50  share a common chip containing the transceiver and controller logic. In one embodiment, the transceiver and controller are both on board the same chip used in the remote units but the controller portion is supplanted, replaced, or augmented by additional programmable controller functionality such a personal computer. In many embodiments of the present invention, the master controller or controllers may require additional programmable functionality relative to the functionality required on the remote units. 
   In one embodiment of the present invention, the transceiver portion of the remote unit can operate in at least three modes. In one mode, the transceiver operates in a very low power “sleep” mode, wherein the transceiver is neither transmitting nor receiving. The transceiver can be awakened from the sleep mode by external control signals, such as provided by control lines coming from the control logic portion of the remote unit. In one embodiment of the invention, only the controller can change the state of the transceiver through the control lines such as control lines  58  and  60  in  FIG. 2 . In a preferred embodiment, at least three events can awaken the transceiver from the sleep mode. One event is the occurrence of a sensor data change, such as a door switch opening, or a significant percentage change of an analog variable. Another event is the lapse of a preset time interval, such as the lapse of the time interval between scheduled health status transmissions by the remote, or between scheduled health status polls by the master unit for which the remote desires to be awake. Yet another event is the resetting of the remote, such as resetting of reset line  68  in  FIG. 2 . 
   In one embodiment, remote units can be configured or programmed to transmit sensor data only on a timeout occurrence or on a change occurrence. For example, a temperature sensor may be configured to transmit every half-hour or upon a one (1) degree change from the last transmission. This can greatly reduce power consumption. 
   In one embodiment, the controller portion of the remote unit can run in a low power mode, but is able to processes external signals and interrupts. In one embodiment, timing is handled by timers on board the chip housing the transceiver and controller. In this embodiment, the controller logic is able to process timing functions while in a low power mode. In another embodiment, timing is handled by circuitry external to the microprocessor, with the microprocessor being able to respond to interrupts but not being able to handle the timing functionality. In this embodiment, the timing can be handled by an RC timer or a crystal oscillator residing external to the microprocessor, allowing the microprocessor to lie in a very low power consumption mode while the external timing circuitry executes the timing functionality. In one embodiment, the timing and microprocessor circuitry both reside on the same chip, but can run in different power consumption modes at the same time. In one embodiment, the remote, not including timing circuitry, initializes in a normal power consumption mode, sleeps in a very low power consumption mode, which, when interrupted, executes in a normal power consumption mode while transmitting or receiving. 
   Referring now to  FIG. 4 , one method, process, or algorithm  150  according to the present invention is illustrated in a state transition diagram. Process  150  can be used for operating a remote unit such as remote unit  50  illustrated in  FIG. 2 . Process  150  can start with an OFF state  100 , where the remote unit is powered down, for example with a dead or removed battery. Upon application of power, such as installation of a battery, a POWER-UP event  101  can be sensed by the microprocessor or external circuitry, causing a transition to a WAITING FOR RESET state  102 . A reset button is installed in many remote units for the purpose of allowing re-initilization of the remote unit by the person installing the unit. In one embodiment, reset can also be accomplished via software, which can be useful if the remote ever becomes confused or has not heard from the master unit for a long time period utilizing a watchdog timer. A RESET event  103  can cause a transition to an INITIALIZING state  104 . While in INITIALIZING state  104 , typical initialization steps can be executed, such as performing diagnostics, clearing memory, initializing counters and timers, and initializing variables. Upon completion of initialization, indicated at  105 , transition to a GETTING SLOTS state  106  can occur. GETTING SLOTS state  106  is discussed in greater detail below, and can include receiving a time slot for communication with the master and receiving frequency slots for transmitting to, and receiving from, the master. In one embodiment, the frequencies to utilize in the next transmission and the time remaining to the next transmission are determined or obtained by the remote unit in the GETTING SLOTS state. Upon completion of the GETTING SLOTS state, indicated at  107 , the process transitions to a SLEEPING state  108 . 
   SLEEPING state  108  is preferably a very low power consumption state in which the transceiver is able to neither transmit nor receive. In SLEEPING state  108 , the controller circuitry or microprocessor is preferably in a very low power consumption state as well. While in SLEEPING state  108 , the remote unit should be able to be awakened by timer interrupts or device sensor interrupts. In a preferred embodiment, the remote unit stays in SLEEPING state  108  indefinitely until awakened by an interrupt. Upon reception of a SENSOR event  109 , a transition to a TRANSMITTING ALARM state  110  can occur. During this transition or soon thereafter, the transceiver can be switched to a transmit mode. While in this state, an alarm transmission is performed, for example, on the transmission frequency determined in GETTING SLOT state  106 . While in this state, transmission of other status or security information can also be performed. For example, the remote unit can transmit the length of time a contact has been open or the current battery voltage. Upon completion of transmission, indicated at  111 , a WAITING FOR ACKNOWLEDGE state  112  can be entered. While in this state, the transceiver can be switched to a receive mode at a receive frequency determined during GETTING SLOT state  106 . While in this state, the remote is typically in a higher power consumption state relative to SLEEPING state  108 . Upon reception of an ACKNOWLEDGEMENT from the master unit, indicated at  113 , the remote unit can enter SLEEPING state  108  again. If an acknowledge is not received within a TIMEOUT period, indicated at  151 , the alarm can be transmitted again, in TRANSMITTING ALARM state  110 . A number of re-transmissions can be attempted. The bi-directional nature of the remote units allows use of the acknowledgement function. The acknowledgement feature can remove the requirement of some current systems that the remote unit broadcast alarms at high power, repeatedly, and for long time periods. Current systems typically do not have remote units that know when their reported alarm has been received, thus requiring repeated transmissions and high power transmissions, even when a low powered, single alarm transmission by the remote could have been or had, in fact, been received. 
   SLEEPING state  108  can also be exited upon reception of a TIMEOUT event  115 . In one embodiment, a timer is loaded with a time period determined during GETTING SLOT state  106 . In one embodiment, a time to wait until transmitting status information, such as 300 seconds, is received from the master unit during GETTING SLOT state  106 . The time to wait can either be used directly or adjusted with a margin of error to insure that the remote unit is not sleeping when the time period has elapsed. For example, a 360 second time to wait can be used in conjunction with a 5 second margin or error to awaken the remote unit for a receiving period from 355 seconds to 365 seconds. After reception of a TIMEOUT event  115 , a status communicating step  114  can be executed, which can include setting the transceiver to either a transmit or a receive mode, discussed below. 
   In one embodiment, a WAITING FOR POLL state  116  can be entered, and the transceiver is set to a receive state at a receive frequency. In this embodiment, the remote does not transmit health status until polled by the master unit. The remote can remain in WAITING FOR POLL state  116  until time elapses, whereupon the remote unit can return to SLEEPING state  108  until the occurrence of the next time period has lapsed. Alternatively, during the WAITING FOR POLL state  116 , the master may transmit a wait instruction that simply indicates that the remote should return to the SLEEPING state  108  for a predetermined period of time. This type of instruction can be used, for example, when the data provided by a particular sensor is no longer needed or is less important in the current system mode. It is contemplated that the system mode can be changed on the fly, whereby the particular sensor may again be polled more often. 
   In one method, a POLL REQUEST  117  is received from the master unit and the remote unit transitions to a TRANSMITTING HEALTH state  118 . While in the TRANSMITTING HEALTH state  118  or soon before, the remote unit transceiver can be put into a transmit state at the desired frequency. In one embodiment, the poll request includes the desired transmit frequency to use. 
   The health status and sensor data and sensor type of the remote unit can be transmitted. In one embodiment, a simple signal can be transmitted containing little information. In another embodiment, more information is included in the transmission. Information that can be transmitted includes remote unit ID, battery voltage, received master unit signal strength, and internal time. 
   In some embodiments, sensor data is included in the TRANSMITTING HEALTH transmission. For example, in a room temperature sensor, the temperature can be transmitted as part of the health or status message. In this way, the periodic message used to insure that the remote unit is still functioning can also be used to log the current data from the sensors. In some embodiments, the data is too energy intensive to obtain and only remote unit health information is transmitted. After completion of the TRANSMITTING HEALTH state  118 , indicated at  119 , a WAITING FOR ACK state  120  can be executed. A WAITING FOR ACK state is executed in some embodiments to await an acknowledgement and/or a synch signal. A synch signal can be used to reset an internal timer to be used in determining the next time to awake from SLEEPING state  108 . A synch signal can be used to prevent small remote unit timer inaccuracies from accumulating into large inaccuracies over time and allowing the remote unit timing to drift from the master unit timing. In some embodiments, an acknowledge signal received from the master unit is used to reset the time interval used by timeout event  109 . In some embodiments, the acknowledge signal includes a new time and/or frequencies to be used by the remote unit for the next SLEEPING state and transmission and receiving states. In this way, the master unit can maintain close control over the next health transmission time and the next receiving and transmitting frequencies. After reception of the ACK or synch signal indicated at  121 , a CALCULATING NEW TIME state  122  can be executed, for determining a new time to be used to determine the timing of event  115 . 
   In one method according to the present invention, after expiration of a timer, a TIMEOUT event  155  occurs which can lead to execution of TRANSMITTING HEALTH state  118  rather than WAITING FOR POLL state  116 . After occurrence of event  155 , the remote unit can immediately transmit health data. In some embodiments, new transmission times, transmission frequencies, and flags indicating whether to wait for master unit polling are included in acknowledge or synch messages transmitted from master to remote. 
   Execution of TRANSMITTING HEALTH state  118  and subsequent state are as previously described. In one embodiment, the decision of whether to generate TIMEOUT event  115  or  155  can be made in the remote, in response to a message received from the master. The process utilizing event  155  is preferred. The process utilizing event  115  is illustrated as an alternative embodiment suitable for some applications. 
   Remote units utilizing the present invention can thus remain asleep in a very lower power consumption mode, neither receiving nor transmitting. One aspect of the present invention making this possible is the coordination of timing between master and remotes. Specifically, when the remote awakes and is able to receive over a window of time, the master should know the start time and time width of that time window to be able to transmit within that window if such a transmission is desirable. Specifically, when the master has allocated a time slot or window for receiving the health of a particular remote unit, that particular unit should transit its health within that time window in order to be heard. 
   Coordination between master and remotes can include coordination of what frequencies to use, whether a transmission has been received, what time interval to transmit health data in, and when to begin transmitting the health data. This coordination is preferably obtained with communication between master and remote units. In particular, communication from master to remote can establish which frequencies to use, when to transmit health data, and whether the last transmission of a remote was received by the master. The fact that this data can be received by the remote means that the remote can react by changing to a different transmitting frequency, changing to a different transmitting power, changing to a different effective time interval or time interval start, and can re-transmit in the absence of an acknowledgment from the master unit. With the time windows for periodic transmission of health data established between remote and master, the remote can sleep in a very low power mode for a high percentage of the time, changing to a higher power mode only to transmit sensor changes and to periodically transmit health or sensor data. 
   In one embodiment, only the master unit is aware of the overall timing or scheduling scheme of the system, with the remotes being aware only of the time until the start of the next scheduled remote unit TRANSMITTING HEALTH state or the time until the start of the next remote unit WAITING FOR POLL period. In this embodiment, the amount of processing power required in the remote is held down while only the master is aware of the overall scheduling of time slots. 
   Adding receivers to the remote units allows adjustment of frequencies in response to communication difficulties. In a typical building installation, remote units are installed near doors and windows and a master unit is installed, often in a central location. Over time, especially in a commercial building, furniture, walls, doors, and dividers are added, which can attenuate RF radiation transmitted through the building, between remote and master units. Reflections can also occur, causing Raleigh cancellation at certain frequencies, greatly reducing the effectiveness of communication at certain frequencies at certain locations, such as in corners. Using bi-directional communication between master and remote units allows adaptive selection of frequencies over time without requiring any work in the field with either master or remote units. 
   Referring now to  FIG. 5 , another aspect of the invention is illustrated in an arm-disarm process  200 . The process can begin in a RECEIVING state  202 . Any receiving state should be suitable to serve as receiving state  202 . In one embodiment, a receiving state immediately after a periodic health status transmission is used as a receiving state. In one embodiment, a receiving state immediately after a sensor change transmission is used as a receiving state. In another embodiment, a periodic WAITING FOR POLL state is used as a receiving state. Upon receiving an ARM message  203 , an ARMING state  204  is entered during which the security device can be armed. “Arming” a security device can refer to various processes for various devices. In general, arming a device refers to making some aspect of the device active, and often refers to making a device active where the active device consumes more power than the inactive device. Referring again to  FIG. 5 , when a DISARM message  207  is received by the remote unit, a DISARMING state  208  is entered and the device disarmed. When disarming processing is done, indicated at  209 , RECEIVING state  202  can be returned to. 
   One reason for disarming a device is to conserve power in a remote battery powered device. Some devices, such as continuity switches may use only a small amount of power when active. Other devices, such as infrared motion detectors may use a larger amount of power when active. In either case, some power can be conserved by disarming the device to an inactive state. When a building or house is occupied, it may be desirable to disarm many if not all of the security devices. 
   One reason for disarming a device is to reduce the number of alarm event transmissions made by the device. This can reduce RF traffic and also conserve battery life, as power is not used for transmitting messages as often. In one example, door switches are disarmed during the day on doors that are to be in use, and are armed during the evening, when the building is closed and secured. In another example, some higher power devices are armed only when verification is required. For example, a remote microphone device may be armed only when listening to follow up on a motion detector alarm or a door open alarm, or a temperature measuring device may only be armed when a temperature reading is desired, and disarmed the remainder of the time. 
   Referring now to  FIG. 6 , an alarm confirmation aspect of the invention is illustrated in a conformation process  230 . Process  230  can be used when reconfirmation of a previous message or event is desired. While in a receiving state  232 , reception of a CONFIRMATION or RE-READ message  233  can cause a transition to a READING SENSOR or RE-READING SENSOR state  234  in which a sensor is read or polled to determine its value. Upon completion of reading the sensor, indicated at  235 , a TRANSMITTING DATA state  236  can be executed in which the desired data is transmitted to the master unit. Upon completion of transmission, indicated at  237 , a RECEIVING state can be entered again. In preferred embodiments, completion of transmission requires reception of an acknowledgement message from the master controller. 
   Confirmation or re-read requests as illustrated in  FIG. 6  can serve to greatly reduce the number of false alarms issued by a security system. In one example, when an alarm event is received by the master unit, the type of sensor is looked up by the master unit, or in some embodiments, is included in the message transmitted by the remote device. In the master unit, a lookup table is used in one embodiment to determine whether confirmation should be requested, how soon, and for what number of repetitions. In one example of the invention, a message is received from a remote unit indicating the opening of a window. The lookup table for that type of device indicates that two readings are required and that the second reading should be taken in 0.5 seconds. The acknowledgment message to the remote includes a reconfirmation request. The remote unit reads the window sensor again after 0.5 seconds and transmits the value to the master unit. The master unit can then report out that the window opened if both readings agree. In the case of a motion detector, a set number of readings over a set time period may be required to report motion to a central reporting service. 
   In some embodiments, a local alarm is sounded for a grace period to allow an occupant to reset the alarm panel before sending an alarm to a central location. In some embodiments, each type of security sensor type is given a weight and a total weight threshold must be crossed before an alarm is reported. For example, a motion detector and either a door opening or a window opening is required to report an intrusion, or at least two different motion detectors must be tripped before an alarm is reported to a central agency. In another example, each alarm event can be given a weight and the system as a whole can have weight decayed or removed over time. In one example, each motion detecting event is given 1 point and each door opening event given 5 points, with the system removing 1 point per 60 seconds, with 6 points required to report out an alarm. The intelligence can be programmed or configured into a master unit, and changed from time to time, without requiring physically or locally changing the programming of the remote units. The system, master unit, and remote unit programming or configuring can be varied from application to application as well. This can be a function of the level of security desired and the relative costs of false alarms to the user. 
   Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate that the teachings found herein may be applied to yet other embodiments within the scope of the claims hereto attached.