The OSI-RE-SS is usually a reflector- type linear optical beam smoke detector made to function like a element of fire alarm techniques. The beam operates primarily on the theory of light obscuration utilising an Infra-Pink beam. OSI-R-SS is really a four-wire conventional reflector-form linear optical beam smoke detector for use https://www.firesense.co.uk/type/conventional-fire-system/conventional-beam-detectors/