CENTRALLY LOCATED ACCESS ALARM SYSTEM

摘要

Apparatus for monitoring a plurality of remotely located doors or conditions in a building. A separate sensor is positioned adjacent each door or at each location at which a condition is sensed. Each sensor or group of connected sensors has a resistor which is connected to a centrally located detector circuit by means of a separate pair of electrical conductors. Each sensor includes means for disconnecting the resistor from the connected pair of conductors either when the adjacent door is open, when some other monitored condition is sensed, or when the sensor is tampered with. The detector circuit includes two relaxation oscillators. The resistor in one or more sensors forms a portion of an RC timing circuit in a first of the oscillators. A change in the resistance in the sensor changes the operating frequency of the first oscillator to cause the second oscillator to cycle and trigger an alarm.