The OSI-RE-SS is often a reflector- variety linear optical beam smoke detector created to operate to be a part of fire alarm systems. The beam operates totally on the theory of sunshine obscuration utilising an Infra-Purple beam. OSI-R-SS is a 4-wire conventional reflector-style linear optical beam smoke detector for use https://www.firesense.co.uk/type/conventional-fire-system/conventional-beam-detectors/