Abstract: A fire alarm system which makes fire determination based on a novel idea which considers various changes of the physical phenomena in the surroundings caused in relation with the occurrence of a fire in terms of changes of vectors. These changes in the physical phenomena are detected by the detecting section in the form of analog data and processed by a data sampling section as sampled data and stored in a storing section in such a manner as discriminating them by the detecting sections. The tendencies of the changes are computed in a first computing section and the vectors representing the present or future conditions of the physical phenomena are computed from the sampled data. The vector is compared in a comparing section with a preliminarily set data related to the fire detection and when the relation therebetween is not a predetermined one, an alarm is given through an alarming section.

Abstract: A parallel bus alarm system in which address signals are represented by successive voltage steps, and responses are represented by current increments. Each alarm element, in response to its addressing, controls a variable current increment to flow in the bus, the magnitude of the current increment being a function of an associated analog measurement to be reported. Each alarm element also causes a predetermined current increment to flow in the bus in response to a condition arising which requires reporting, the total current change thus being directly proportional to the number of alarm indications.

Abstract: An interface for generating a serial bit stream corresponding to one or more switch settings and transmitting that bit stream to a polling circuit. Four parallel bits representing a setting of a decimal switch are converted to serial bit sequence. This sequence is preceded by a start bit and followed by an extended stop bit. In an embodiment where multiple switches are polled, the data sequence is followed by a switch designating sequence and then the extended stop bit.

Abstract: A telemetry system for a surface maintenance machine such as a scrubber or a sweeper has a plurality of sensors which monitor machine operating conditions. The sensors are periodically scanned and repetitive outputs indicative of sensor condition are used to provide tone coded telemetry signals. The tone coded signals are modulated on a suitable carrier frequency and are sent to a receiver which is remote from the sensors. The receiver decodes the tone coded signals to provide a display of the conditions being monitored by the sensors. The tone coded outputs from the transmitter also include an identification of the particular machine which is providing information for the display at the receiver.

Abstract: A document processing system for reading a line of MICR data from documents passing along a document track and for generating a marker to be positioned over a character which was not read properly when that line of MICR data is presented on a display. A special thresholding circuit is used to convert the image data of the line of MICR data to binary data. The circuit automatically adjusts for changes in light intensity at the associated scanning line where the image data is generated.

Abstract: A device for generating an alarm signal in the event of an environmental abnormality has multiple sensors, with a multiplier associated with each sensor, an adder, and a comparator. The sensors are disposed in respective sensing volumes, which may be different. The sensors detect a level of smoke, heat, gas or other environmental abnormality within each sensing volume, and convert the level into an electrical analog signal. The associated multiplier multiplies a coefficient proportional to the sensing volume for the associated sensor with the analog signals from the sensor. The adder adds the outputs of the multipliers. The comparator generates an alarm signal at an output thereof when the output of the adder exceeds a predetermined value.

Abstract: A self-powered sensor for a closed-loop security system includes a self-powered sensor network which provides a switch-actuating signal upon the detection of a physical condition. An electronic switch, which is in a normally closed position, is connected between the positive and negative poles of a closed-loop security system and opens the loop upon receipt of the switch-actuating signal thereby triggering an alarm. The self-powered sensor network may include a voltage doubler for converting the AC output of a transducer to a DC voltage of an amplitude sufficient to open the switch. When the switch is opened, voltage from the closed-loop security system becomes available to power a visible or audible alarm identifying the sensor that opened the loop.

Abstract: A communication system in which a controller ordinarily polls addressable transponders in a sequential or random manner normally allows the transponders to respond only in their respective assigned time period. Certain of the transponders are connected to allow response in a predefined time segment from those transponders so connected if (1) the transponder is in fact programmed for response during this predefined time segment, and (2) the predefined time segment is now occuring. By providing the predefined time segment at the same position in the response time period of each transponder, a "public time" is provided to allow virtually instantaneous identification and verification of a high priority interrupt (such as a holdup alarm). In addition the transponders programmed to respond during public time on a high priority basis can be subdivided into separate groups, and the groups can be identified at the controller.

Abstract: The present apparatus relates to nonvolatile fault flags for use in aircraft. The term "flag" refers to an electromechanical indicator which displays a human-readable signal which identifies a fault. A fault is a malfunction occurring in the aircraft. The term "nonvolatile" refers to the feature that the signal is not lost when electrical power is terminated to the indicators. In addition, apparatus are provided for displaying the first, and only the first, fault signal received by the indicator, and for the prevention of triggering of the indicator by spurious signals.

Abstract: A fence having security wires fastened to posts via sensors and having an electronic evaluation circuit connected to the sensors, which releases an alarm signal when one of the sensors signals a contact of the security wire which is connected to it. Each sensor has a housing fastened to a post, a holder connected to a security wire and a transformer placed between housing and holder, which produces a signal which is approximately proportional to the position of the holder. An alarm signal is generated when one or only a few security wires move slowly, yet such slow movements are ignored when caused by environmental factors. A highly reliable security fence is thus obtained.

Abstract: A detector system having multiple sensors, each sensor detecting a different danger condition, has an address comparator for determining whether an access address coincident with a selected address is present in an access signal received from a central monitoring unit. The detector exchanges an information signal with the central monitoring unit using the coincidence detection signal of the address comparator. Success coincidence detection signals, corresponding to successively selected addresses being present in the access signal, are counted by a counter. If the detector has two sensors, the counter may be a D flip-flop circuit, and if the detector has more than two sensors, the counter may be a ring counter. The counter generates a signal for operating respective analog switches connected to the outputs of each sensor so as to successively through-connect the output of one sensor to the output of the detector system for transmittal to the central monitoring unit.

Abstract: An analog fire detecting system in which a plurality of sensors produce analog data corresponding to a physical state such as temperature, smoke density, etc. relevant to a fire condition. The values of such analog data are compared with a predetermined threshold level, and if the threshold level is exceeded the analog data is transmitted to a central station in response to a polling signal therefrom. A CPU in the central station determines, from the analog data from the sensors, if there is a possibility of a fire and if so makes a predictive calculation of the remaining time until a fire condition will be reached. An alarm is given when such predicted time falls below a preset interval.

Abstract: A composite detector includes a plurality of sensors of the same or different types, a plurality of analog switches connected to outputs of the plurality of sensors, and an operation circuit, such as an operational amplifier. The sensors detect physical phenomena such as heat, smoke and gas according to different principles of detection, and output analog detection signals. The analog switches are controlled by a selector operated with a control signal from a central monitor or magnitudes of outputs from the plurality of sensors. The operation circuit calculates outputs from the plurality of analog switches.

Abstract: A pulse accumulator network for receiving a plurality of pulse trains wherein each pulse train includes a plurality of pulses. The pulse accumulator network accumulates the pulses in each of the received pulse trains and the pulse accumulator network outputs each of the accumulated count of pulses in response to receiving polling signals. The pulse accumulator network is adapted to be utilized in a flow monitoring system, for example, wherein the pulse trains are flow signals indicative of the velocity of the fluid flowing through one of the monitored flowlines.

Abstract: An information reporting system is disclosed wherein a plurality of remote stations each receive synchronization signals from a master station, the synchronization signals initiating a timing mechanism in each remote station for dictating the time slot in which each remote station can transmit its information, each time slot occurring at a substantially different point in time, a master station having a synchronization generator for generating the synchronization signals and an indicator for indicating the information received from the remote stations, and a communication channel for interconnecting the remote stations and the master station.

Abstract: A circuit for controlling a receiver in an implanted device and circuitry for decoding and storing received program signals is disclosed. In the circuit a control circuit periodically activates a receiver to surveil for remotely generating programming signals. When a program signal is detected by the receiver the control circuit latches the receiver into a continuously activated state for a predetermined time interval. If a reset code is detected from subsequently received signals the receiver is held in an activated condition for a further predetermined time interval. Decoding circuits including a timer are reset upon receipt of the refresh code and provide control over sequences of received programming data for use in programming the stimulation mode of output circuits in the implanted device.

Abstract: An improved apparatus for detecting environmental disturbances such as the occurrence of a fire, a gas leak or the like, includes a central processing unit and a plurality of terminal detectors, wherein an identification code is assigned to each of the detectors and the central processing unit sequentially calls the detectors in rotation requesting them to transmit thereto the data collected on smoke concentration, gas concentration, temperature or the like. The apparatus is provided with a display unit and a memory. Data collected by each detector concerning on the environmental condition of the place where each detector is installed are stored in the memory in time series. When a signal for data exceeding a fixed reference level is received, a provisional alarm is raised for the operator and the stored data for a limited period of time in the past are displayed.

Abstract: A central protection system suitable for the protection of a building from fire and other hazards includes a set of environmental sensors and circuitry for interrogating the sensors. The system also includes communication and control lines, as well as monitoring circuitry having individual channels coupled to respective ones of the communication and control lines. An inaudible pilot tone of subsonic frequency may be coupled to a communication line, and the corresponding channel of the monitoring circuit includes a detector of the pilot tone. A circuit for the generation of evacuation signals and fire brigade signals is composed of two sections coupled in tandem, and includes sequencing circuitry for the recycling of tones produced by the respective sections.

Abstract: In a polling type surveillance control apparatus for a security system, inherent addresses are assigned to respective terminal devices such as smoke detectors, temperature sensors, gas leakage detectors, fire partitions and smoke dampers. When a self address detector in the terminal device detects a coincidence between the address signal from a central station and a preset self address, the terminal device indicates it has been accessed or energized and power control thereof may also be performed.

Abstract: A monitoring system of the type suitable for use in monitoring signals from security installations or networks includes a central control station serving a plurality of users and to which the users are connected by an existing telephone network or some other form of direct or switched line connection. Each user is provided with an encoder in the form of a combined control unit and digital telephone dialler, said encoder being programmed with information concerning each user in principally alphabetical character form to increase the likelihood that the message will be received and understood even in the event that certain characters contained in the message are missing. The control station is equipped with means for receiving and decoding the message transmitted from the user's control unit together with visual display means, such as a VDU or line printer, for visually displaying the received message.

Abstract: Given a device for contact-free position measurement, a movable or resting part that represents a load in an alternating field or that is designed as an element emitting field lines is spatially neighbored by a sensor carrier that exhibits a plurality of individual sensors that are electrically and spatially separated from one another, whereby each of said individual sensors can be applied to direct or alternating voltage, and whereby an interrogation and evaluation means is provided, to which each of the individual sensors is connectable for the purpose of identifying its output signal that is dependent on the position of the positionally variable or resting position indicator.

Abstract: In a theft protection system, particularly for a shop area, several exit passages with individual antenna systems are surveyed by means of a single transmitter for the transmission of electromagnetic interrogation signals and a single receiver for reception of resonance signals generated by unauthorized removal of a good, the antenna system for all the exit passages being connected to the transmitter and the receiver through multiplexers. A central control unit controls the multiplexers so as to actuate the antenna systems in successive time frames, whereby only one antenna system is made operative at a time. With each exit passage is associated an alarm device which is only activated for an alarm release from an alarm-actuating circuit connected to the control unit in case of compliance with at least one positive and one negative alarm criterion.

Abstract: A plurality of different types of operating systems in buildings organized in geographical groups, each group having a local service office, are monitored at both the local offices and central office for the presence of performance conditions and conditions indicative of an alarm condition.

Abstract: Equipment for monitoring combat vehicles, especially tanks, firing practice firing with simulated rounds. Each combat vehicle has a laser that emits a pulse of light when the firing button is pressed and devices to receive and display an arriving pulse of light. A television pickup is coupled to a monitoring or targeting device in each combat vehicle and can be connected through a video section with a television monitor at a director's post. At the director's post there are at least two television monitors, each assigned to a given group of combat vehicles. As long as none of the firing buttons in any of the combat vehicles are pressed, the image supplied from the monitoring or targeting device in a selected combat vehicle will appear on each television monitor. When a firing button is pressed in one of the vehicles, the image supplied from the monitoring or targeting device in that vehicle will appear on the monitor associated with the vehicle for a predetermined period of time.

Abstract: A soil pollution monitoring system includes a plurality of ducts for conveying gases and air past a sensing device. The sensing device detects selected compounds in the gases and air and provides an output in electrical form which indicates whether or not the levels of certain compounds in the gases and air are greater than a threshold amount thereby indicating that a leak has occurred.

Abstract: Measuring stations or locations are connected in cascade to signal lines and transmit measured or measuring values to a central signal station at which the measured values are linked or appropriately processed so as to obtain distinct malfunction or alarm signals. Upon activation of the monitoring system all measuring stations are disconnected by a change in voltage appearing on the signal line. Then, the measuring stations are reconnected to the signal line in a timewise staggered fashion by means of switching elements present at each measuring station in such a manner that each measuring station additionally reconnects a subsequent measuring station to the line voltage after a predetermined time-delay. Address storages are present at the measuring stations and are charged or occupied in a predetermined sequence by the central signal station with addresses associated with the individual measuring stations.

Abstract: A system for sensing multiple conditions, such as alarm conditions, at each of a number of remote stations, the sensing being accomplished solely through a pair of power lines by means of which the remote stations are connected in a cascade arrangement with a central station. When power is applied to the first of the remote stations, a current pulse is drawn through the power lines and is modulated in accordance with a sensed condition at the remote station. At the end of the current pulse, there is at least one zero-current interval, the duration of which is varied in accordance with another sensed condition at the remote station. The central station, after applying power to the first remote station, identifies the sensed conditions from the modulated current pulses and the durations of the zero-current intervals. Each remote station also includes a line power switch that remains open until the completion of interrogation of the sensed conditions at that particular station.

Abstract: Apparatus for detecting the presence of intruders includes a plurality of sensors. The apparatus not only operates an alarm to indicate the presence of an intruder, but, also, identifies the location in which the intrusion has occurred. There are two groups of sensors at each discrete location or zone. One group of sensors detects the presence of an intruder by the activation of one or more sensors. Another group of sensors discriminates against externally generated sounds to reduce false alarms. In the preferred embodiment, both groups of sensors utilize the same cable. An intrusion detection multiplexer and a discriminator multiplexer are employed to enable the sensors of each zone respectively to be sequentially detected and identified through the same apparatus.

Abstract: A time division multiplex remote control system controls data transmission between a central controller and a plurality of addressable remote terminals coupled to the central controller through a signal line. The central controller transmits to each of terminals a transmission signal comprising address data addressing a terminal, control data, a reply signal standing-by period defining signal for defining a period for receiving a reply signal from the corresponding terminal, an interruption request signal standing-by period defining signal for defining a period for receiving an interruption request signal from the terminal. Each terminal receives the transmission signal and, when the received address data coincides with an address of the terminal, accepts the control data and sends a reply signal during a reply signal standing-by period.

Abstract: A security alarm system has a plurality of sensors for fire, smoke, intrusion and appliance operation. A central monitor is provided for monitoring and perceptibly indicating the status of each of the sensors. To provide for communication between the sensors and the central monitoring system, transmitters are located on the sensors and a receiver is provided on the central monitor. When one of the sensors establishes an alarm condition, its transmitter is actuated to transmit information indicating the type of alarm. A portable keyboard loads information data into an electronic memory of each of the transmitters and into the electronic memory associated with the receiver. The keyboard is separable from each memory to preclude altering of the information stored in the electronic memory of the respective transmitter.

Abstract: An atmospheric abnormality detection system includes a command discriminator and a display/alarm circuit in each sensor terminal. When the command discriminator receives a coincidence signal from an address comparator, the command discriminator causes an A/D converter to convert an analog sensor output to a digital signal as response data. When an abnormal state display command is transmitted from a main unit to the command discriminator, the command discriminator causes the display/alarm circuit to display information indicating the abnormal state and/or generate an audible alarm.

Abstract: A remote sensing and indicating system for monitoring and displaying at a central operating location the state or position of a remotely located multiple state element. The multiple state element may be a subsea valve which may be either in an open state or a closed state. The system electronically scans valve position switches, stores data indicating the position and drives lamps to display valve position. Switches at the remotely located valve are selectively closed in response to the state of the valve. The switches are connected to the central location by only two leads.

Abstract: An interrogation unit for connecting into an installation via sensing elements connected to sense required information in the installation, said interrogation unit having signal supplying means for supplying signals indicative of the condition of each of various sensors in the installation, and trigger circuit means activatable upon receipt of a request signal to transmit said signals for each of the sensors in turn.

Abstract: A first sensor for the detection of dielectric failure (by burning) within a multilayer printed circuit assembly comprises an isolated conductive layer. This first sensor is connected by a first diode to a single wire which also connects a second, temperature, sensor via a second diode (system ground is a return). A number, nominally 16, of such single wire connected sensor pairs are selectable in accordance with an externally (microprocessor) furnished address. During a first time period, an externally (microprocessor) selected interrogation of temperature causes a first, positive, voltage bias to be applied to the selected sensor pair resulting in a current linear with temperature (over the range of 0.degree. C. to 100.degree. C.) in the second sensor. This current is transformed to voltage, offset by 273.degree. Kelvin, amplified, and converted to a digital value for issuance to an external (microprocessor) requestor.

Abstract: An automatic testing system for testing the operability of transmission line carrier units using timers that periodically activate a signal for energizing local carrier unit transmitters with a delayed energization of local carrier unit receivers, and a signal stepping circuit that connects the transmitter and receiver signal sequentially to the carrier units in a series of transmission lines. The absence of a signal being received by the local carrier unit receiver indicating a fault that is detected in latches that provide an indication of the carrier in which the fault has occurred and an indication at a remote computer when there has been at least one failure in the testing sequence, which failure indication remains activated at the end of a testing sequence to assure attention by the operator. The sequencing occurs automatically with a capacitor-delayed spike signal that provides sufficient time for the indication of the absence of a signal without requiring separate circuitry.

Abstract: A transmitter has a plurality of parallel inputs, and each input is connected to a switch. The transmitter receives a trigger signal that has a constant frequency. Using the trigger signal, the transmitter provides a signal which consists of individual series signals, each one of the series signals representing the status of one of the switches. The series signal also includes a sync signal which precedes the series signals associated with the status of the switches. These series signals are generated in synchronism with the trigger signal that is applied to the transmitter. A receiver receives the series signals and also the trigger signal. The sync signal is detected in the receiver, and a status signal is generated in response to each of the series signals following the sync signal as those signals are received. Each status signal is applied to an input which is identified by the number of repetitions made by the trigger signal after the sync signal is detected.

Abstract: In apparatus for communicating data by repetitively completing and opening an electric circuit, the improvement which comprises a light source inserted in the circuit to provide a visible train of light flashes upon operation of the apparatus, and circuitry for suppressing a predetermined portion of the flashes in response to a condition, to reduce the observable flashing rate of the source.

Abstract: In the monitoring system which is intended for buildings, rooms and objects a multitude of measuring or detecting and signaling stations are series connected to a central signal station. Each of the detecting and signalling stations transmits information about its instantaneous state, which may be any one of standby, warning, alarm, malfunction, to the central signal station by means of an electronic circuit member.

Abstract: A monitoring system for a protection loop that has a plurality of switches in series utilizes modules with inexpensive diodes and resistors, and is conveniently and easily added to existing burglar alarm circuits and loops. A monitoring module that includes a diode and a paralleled resistor is connected across each switch. First and second interrogating signals are alternately applied to the protection loop. First comparator circuit means provides an output in response to each first interrogating signal when one of the monitored switches in the protection loop is open as indicated by the response of the module resistors; and second comparator circuit means provides an output in response to each second interrogating signal when more than one of the monitored switches in the protection loop is open as indicated by the response of the module diodes.

Abstract: A data transmission device having a plurality of monitor units which are wire connected in series to a computer. During a working cycle, one unit after the other is activated by emission of clock pulses from the computer. The clock pulses are counted in an address counter (4) in the respective unit. Upon reaching a count value preset in an address coder (7) a sequential circuit (6) is activated, the latter consisting of a binary counter (3) and a functional decoder (5) connected thereto. At the same time as clock pulses corresponding to the address of the unit are received via a clock pulse connection ("clock"), a pulse train is emitted via switches (A,B,C,D), the positions of which corresponding to sensed information bits, to a data transmission connection ("data"). The outputs of the sequential circuit (6) are also connected to a control circuit (9) for generating control signals to the particular monitor unit or a sub-system connected thereto.

Abstract: A fire alarm system having a plurality of fire detectors connected in parallel with each other to a pair of power/signal lines leading to a central signal station and adapted to respond to the signal station with a detection signal in the mode of current and controlling the signalling between the fire detectors and the signal station. The detection of a fire is accomplished by computing a difference between a steady-state current flowing through the signal lines and a detection current which are detected in an analog amounts. Each of the fire detectors is called by a simple calling clock pulse whose transmitting timing is controlled by a microcomputer of the central signal station to transmit a detection data. The generation timing of the calling clock pulses is freely selectable to effect a desired control of the fire detectors.

Abstract: In an alarm system a central signal station periodically transmits interrogation signals, preferably in the form of infrared radiation packets to remotely located detectors which transmit a response signal back to the central signal station after differing time delays that are characteristic for the individual detectors and which permit the localization of the source of the response signal. In an alarm state, the detectors respond to every interrogation signal, in the normal operational state to only every m.sup.th interrogation signal, i.e. less often, and in a state of diminishing battery potential to only every small p.sup.th interrogation signal, i.e. even less often. The state of the individual detectors is determined from the frequency with which the response signals are transmitted back by the detectors, that is the ratio of the response signals to the interrogation signals.

Abstract: Each object on a panel has a respective location designated by an address and associated with an indicator lamp. A panel managing system comprises a memory for successively reading location address combinations. The indicator lamps are successively energized at the locations designated by the addresses read from one and the same combination so that a collector withdraws or inserts the objects at designated locations. The objects are detected to check the normal presence or absence of the objects in the panel after withdrawal or insertion of each object.

Abstract: A device for monitoring the condition of a plurality of remote stations is particularly suited for monitoring the condition of smoke alarms, television antitheft devices and the like in hotels and similar institutions. The device includes a plurality of remote sensors wherein each sensor has a predetermined electrical characteristic, such as a predetermined electrical resistance, and at least one remote sensor is associated with each remote station. A main control unit sequentially measures the electrical characteristic of each of the sensors and then compares the measured electrical characteristic from the sensors with a predetermined value. In the event that the measured value differs from the predetermined value by more than a preset amount, an indicator is activated which advises an operator which sensor, and thus which remote station, has been activated or tampered with thus requiring investigation.

Abstract: In a method for controlling output of alarm information in a system for monitoring a plant wherein process variables including analog type process variables at respective sensing points in the plant are sampled and each of the sampled analog type process variables is compared with a normal range limit value for determination as to whether it is within a normal range or within an abnormal range, an alarm limit level is determined in accordance with changes that have occurred in the process variable during the latest sampling interval. Output of alarm information is permitted in connection with the process variables that have a priority level whose value is higher than the value of the alarm limit level.

Abstract: A method and apparatus for monitoring an alarm system such as a fire alarm system having a plurality of alarms connected to a central station determine the amount of departure of measured alarm values from a rated quiescent value and calculate a fluctuation value therefrom, the fluctuation value then being compared at selected time intervals with a rated limiting value. If the result of the comparison shows that the fluctuation value is less than the rated limiting value, a malfunction signal is displayed.

Abstract: A data distribution apparatus for controlling the distribution of data signals from field mounted devices to a central processor includes a backplate having wiring connected thereto between the backplate and the field mounted devices and between the backplate and the data processor. A cover for the backplate includes a printed circuit board mounted thereon with an electrical connector extending therefrom. The cover connector is arranged to mate with an electrical connector board mounted on the backplate to selectively connect the printed circuit board on the cover to electrical circuits connected to the connector board on the backplate. Thus, the removal of the cover which is keyed to the backplate to ensure a correct orientation thereof on the backplate is effective to interrupt the electrical connections provided by the printed circuit board among the wiring connected to the electrical connector board and vice versa.

Abstract: A security system continuously monitoring a plurality of spatially diverse events which are reportable to a central monitoring facility, the system including a controller for sequencing the performance of reporting and monitoring tasks according to the requirements of the events. The system also performs the tasks according to a predetermined priority, in particular, alarm message queuing. In addition, alarm conditions and system operation are verified by specified communication procedures and redundancies. Furthermore, system communications capabilities include keyboard entry and output display and an interrupt facility.

Abstract: Each sensor of the system is connected to a central station and is interrogated cyclically. In turn, the sensors generate over a bus line a variable amplitude signal synthesized from data stored in a read only memory. Each sensor has a read only memory with different data and thus generates a different waveform during successive intervals of time. Any modification in the waveform of the signal transmitted by a sensor is interpreted as an alarm due to the detection of an intrusion, for example, or due to an attempt at sabotaging the sensor or the bus lines. The complexity of the waveforms synthesized by the sensors makes a simulation very difficult intended to neutralize the remote monitoring system.

Abstract: A plurality of remotely located transponder units each communicate with a central station unit to provide a full array of alarm and status signals to the central station. The transponder units are capable of remotely addressing the central station unit directly, without the need for human intervention at the central station, to alter subscriber opening and closing times, passwords, and other system parameters. The transponder also permits defective zones to be shunted either from the central station or locally pending repair, testing and status checks.