Optical Smoke Alarms are recommended by British Standard 5839-6 for circulation areas. Detas Optical Smoke Alarms incorporate the latest optical sensing technology, which is more sensitive at detecting large particles of smoke which tend to be produced in greater amounts by slow smouldering fires. Suitable for use within hallways and landings, as well as living rooms and bedrooms. This is the new range of Deta alarms. These alarms ARE NOT compatible with previous ranges of Deta or any other brand of smoke alarms, therefore should only be used in new installations. These alarms can be installed, along with linked heat alarms (if required), to provide a fire detection system to comply with British Standard BS 5839: Pt.6 Grade D System incorporating one or more interlinked mains powered smoke alarms and heat alarms (if required), each with an integral stand-by supply. Wiring requirements:- 1.0mm or 1.5mm 6242Y Twin & Earth cable to the first alarm position, then 1.0mm or 1.5mm 6243Y 3 Core & Earth cable from the first alarm position to the second alarm and so on in a "radial" or "daisy chain" type circuit arrangement.