Mains 230/240V AC Ionisation Smoke Alarm with 9V alkaline battery back up (included). This alarm is interconnectable with up to 20 other alarms, meaning if one sounds, all sound. It features a built-in Test / Hush button and a memory function that indicates if an alarm has been previously activated. It also has a one-person test feature and a low battery warning. The alarm is Kitemarked to BS EN14604:2005 and can be interconnected by hard wiring or used with Aico radio wireless bases.