The OSI-RE-SS is actually a reflector- variety linear optical beam smoke detector intended to run being a part of hearth alarm methods. The beam operates totally on the basic principle of light obscuration utilising an Infra-Red beam. OSI-R-SS is 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/