Mains-powered optical smoke alarm that can be interlinked with up to 23 other Kidde mains alarms, be they ionisation, optical or heat. Once interlinked, the detection of the relevant danger by an individual unit will sound across all the connected alarms. Interlink with up to 23 Kidde Firex hard-wired alarms – all alarms sound if danger is detected Mains operation – 9V Alkaline back-up battery supplied as standard Reduced energy consumption – lower lifetime running costs (* compared to previous Firex alarms) Combined Test/HushTM button allows regular testing of alarm function and can be used to temporarily silence nuisance alarms