Abstract: A burglar alarm system of the non-wired perimeter protective type for detecting and indicating break-ins at an entrance or opening, such as a window or door, of a building, employs as a sonic signal generator a transducer that is both triggered and powered by the break-in. The sonic signal is of a specific selected supersonic frequency and is received by a remotely located local receiver within the building which in turn may actuate an alarm. Protection against false activation by sonic noise is provided by altering the gain of the receiver in response to received sonic noise adjacent to but different from the selected frequency, so that noise containing even a strong signal at the selected frequency, as well as at adjacent frequencies, does not result in an alarm being raised, but a weaker signal at the selected frequency, without signals at adjacent frequencies, such as is produced by the transducer, does result in an alarm being activated.

Abstract: An engine rpm sensor utilizes a gas filled lamp for connection to a circu including an engine ignition system and a spark plug. A light pipe is exposed to the lamp and couples an optical signal each time a spark plug is fired to a remote location for utilization in a display or indicating device.

Abstract: A calibration circuit and method for use with systems of the type displaying values of a measured condition in response to electrical pulses received at the system input in which the repetition rate of the received pulses is representative of the value of the measured condition. Electrical pulses, having a known repetition rate are generated for simulating a value of the measured condition in response to a reference signal of known frequency, the repetition rate of said simulating pulses being determined by the frequency of the reference signal.