The OSI-RE-SS is actually a reflector- variety linear optical beam smoke detector built to work to be a ingredient of fireplace alarm units. The beam operates totally on the basic principle of sunshine obscuration utilising an Infra-Pink beam. OSI-R-SS is really a four-wire conventional reflector-variety linear optical beam smoke detector https://www.firesense.co.uk/type/conventional-fire-system/conventional-beam-detectors/