Abstract: An apparatus is disclosed for use in a multi-zone alarm system having a single-pair wire alarm loop and programmable switching circuit arrangements. The apparatus includes a current source serially connected to the single-pair wire loop and selectively operative to provide a predetermined current signal in the loop. A plurality of zone sensing devices are arranged in a normally closed series circuit along the single-pair wire loop. Each of the zone sensing devices is adapted for generating coded voltage changes and alarm activation caused by an open circuit created therein. An element is provided for indicating the condition of each of the zone sensing devices, while a mechanism is provided for selectively arming and disarming the zone sensing devices.

Abstract: The present invention relates to an intruder alarm system which compensates for background and other interfering noises. The system comprises dual amplifiers, one a main channel and the other a control channel wherein the control channel is responsive primarily to background and other interfering noises and develops a control signal which when applied as a control signal to modify the amplification characteristics of the main amplifier effectively removes the effect of the background and other interfering noises from the output of the main channel.