The OSI-RE-SS is usually a reflector- type linear optical beam smoke detector designed to operate as a component of fireplace alarm units. The beam operates totally on the theory of light obscuration utilising an Infra-Red beam. Beam smoke detectors might be a significant ingredient of a nicely-created automated hearth alarm https://www.firesense.co.uk/type/conventional-fire-system/conventional-beam-detectors/