Importance

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Abstract

A security device for determining the opening or closed condition of an access gate, such as a door or window hinged within an opening in a wall, has a detector unit mounted on the wall adjacent to the opening and linked to a remote control unit by a radio transmitter in the detection unit and a radio receiver in the control unit. The detection unit has an infrared generator and an infrared detector isolated from the generator, the detector and generator confronting a reflector mounted on the access gate when the access gate is closed. The reflector is translated from the field of the infrared generator when the access gate is open. The infrared generator is excited by a pulse generator to produce pulses of infrared radiation, and the scattered radiation from the reflector is detected by the infrared detector to produce electrical pulses coincident with the pulse generator. A coincidence circuit determines the presence of the detected pulse, and the absence of coincidence results in the transmission of a radio wave from the detector unit to the control unit to establish alarm conditions.

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First Claim