10-year life mains-powered smoke alarm with a 9V battery back-up. Suitable for all homes, its modern design also features a high performance optical sensor to reduce false alarms. Large central test and silence button makes regular testing and silencing easy. Enhance home protection by interconnecting up to 12 smoke (SW1 or SW10) and/or heat (HW1) units, so when one sounds they all sound. Includes a safety clip feature to prevent installation of smoke alarm without back-up battery installed. Interlinked when Hardwired 230V AC Mains-Powered with Battery Backup Replaceable Lithium Battery Supplied 85dBA Alarm at 3m Test/Hush Button LED Indicators Interlinked when Hardwired 230V AC Mains-Powered with Battery Backup Replaceable Lithium Battery Supplied 85dBA Alarm at 3m Test/Hush Button LED Indicators