The beam operates primarily on the basic principle of light obscuration employing infrared. The OSI-RI detector is usually a mixed transmitter/receiver that could be directly connected to an clever detector circuit in LiteSpeed® or CLIP mode. Undesired alarms a result of the beam getting entirely obscured for a short length https://www.firesense.co.uk/type/addressable-fire-system/addressable-beam-detectors/