The BRKreg; 660MBX Optical Smoke Alarm is mains powered with a 9V alkaline battery backup that will provide power in the event of a mains failure. Thermally enhanced optical technology reduces nuisance alarms. This alarm features a test and alarm pause button, and will also notify you in the event of a low battery. LED operating indicators and an alarm source indicator. It can be connected with up to 12 compatible smoke and heat alarms for simultaneous warning. 5 year warranty. Conforms to BS EN 14604: 2005 Suitable for installations complying to BS 5839-6: 2019 Grade D2