This unit detects initial smoke formation with its sensitive photoelectric system and signal processing circuit giving an alarm signal as an early warning. Photoelectric alarms are less likely to trigger a false alarm from Kitchen or bathroom steam than traditional ionization alarms. This model also has a hush feature to reduce the unit's sensitivity for a ten minute period when needed.Battery[tab]1 x 9V PP3 (supplied)[br]Alarm output[tab]85dB @ 3m[br]Mounting hole centres[tab]70mm[br]Dimensions[tab]34 x 101mmØ[br]Weight[tab]136g (with battery)[br]Static working current[tab]<12µA[br]Operating temperature[tab]-10 to 40°C