The chamber is designed to exclude light from any external source. At an angle to the LED is a 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 chamber, the light pulse from the LED will be refracted into and registered by the photo-diode.
If the photo-diode “sees” smoke on the two following pulses (alarm confirmation), the detector changes into the alarm state. A highly visible external clear LED fl ashes red when the detector is in operational standby and changes to steady red in alarm state. The clear LED allows for easy floor level detector type identification.
Comes with MSB-65B base.