Abstract: A glass breakage detector utilizes a single microphone or piezoelectric element as a transducer to detect both the structurally-transmitted vibrations and airborne sounds indicative of breaking glass. The structurally transmitted component and airborne component are combined in accordance with a time-dependent function to provide an indication of breaking glass which has a low false alarm rate.

Abstract: An intrusion detection system includes housing structure with a radiation entrance aperture, a sensor responsive to infrared radiation mounted in the housing structure. Optical system structure in the housing structure receives infrared radiation through the radiation entrance aperture from a monitoring zone and focuses the received infrared radiation onto the sensor, and means in the housing structure connected to the sensor provides an output signal in response to movement of an infrared radiating object in the monitored zone. Reflector structure of the diffuse (non-optical) type is adapted to be located in a first position immediately in front of the sensor and reflects visible radiation from a source of visible radiation located in a monitored zone and directed in a beam at the sensor back through the optical system to a monitored zone provided by the optical system structure.