The OSI-RE-SS is actually a reflector- sort linear optical beam smoke detector created to function as a ingredient of fireplace alarm programs. The beam operates primarily on the principle of sunshine obscuration utilising an Infra-Purple beam. OSI-R-SS is a four-wire conventional reflector-kind linear optical beam smoke detector to be used https://www.firesense.co.uk/type/conventional-fire-system/conventional-beam-detectors/