The Hager TG501A is an optical smoke detector with a detection range of 50m2. This smoke detector is connected directly to an existing, 230-volt power socket in your ceiling. The detector does have a backup battery, just in case. This means it'll always keep working, even during a power outage. Always put the smoke detector in at least one spot along the escape route, such as the hallway, the landing or the living room. The detector works both by itself and linked up. If you own more Hager smoke detectors and connect them using a cable, they'll all go off simultaneously when smoke is detected. The 85-decibel audio signal will then be audible in every room that has a smoke detector.