The OSI-RE-SS is actually a reflector- type linear optical beam smoke detector intended to operate for a component of hearth alarm systems. The beam operates totally on the principle of light obscuration utilising an Infra-Pink beam. OSI-R-SS is really a four-wire conventional reflector-variety linear optical beam smoke detector for use https://www.firesense.co.uk/type/conventional-fire-system/conventional-beam-detectors/