Series 65 Optical Smoke Detector

Optical smoke detectors incorporate a pulsing LED located in labyrinth within the housing of the detector.  The labyrinth is designed to exclude light from any external source.  At an angle to the LED is photo-diode which normally does not register the column of light emitted by the LED.
    In the event of smoke from a fire entering the labyrinth the light pulse from the LED will be scattered and hence registered by the photo - diode.  If the photo - diode " sees " smoke on the two following pulses, the detector changes to the alarm state when the indicator LED will light up.  The detector housing is identical to that of ionization smoke detector.  It is distinguished from this type by having an indicator LED which is clear in quiescent state but produces red light in alarm.
     The optical detectors are easy to disassemble and clean without the necessity of returning them to the factory.