FAP‑520 Automatic Fire Detectors LSN improved version
Modern, ultra-flat design
Smooth, easily-cleaned detector surface
Innovative fastening mechanism
High reliability
Maintains LSN loop functions in the event of wire
interruption or short-circuit thanks to two integrated
isolators
http://resource.boschsecurity.com/documents/FAP_520_Data_sheet_enUS_9007200510398731.pdf