ALARM SYSTEM FOR SENSING SMOKE AND INTRUDERS

摘要

An alarm system using a laser generated light beam which extends through a plurality of isolated detectors and ends at a control station. Each detector includes two light-to-electric transducers, one for detecting smoke by scattering and the other to detect an intruder by the temporary blocking of the beam. There is no electrical wiring connecting the detector stations. A signal denoting smoke or an intruder is sent over the laser beam in the form of an amplitude or polarization modulation at a characteristic frequency. This signal is received at the control station, its frequency of modulation is determined and an alarm is activated.