This Optical Smoke Alarm is battery powered with a sealed in lithium battery and has a 10 year life. It is a standalone unit which is easy to fit with a twist on base. It features a large test/hush button which enables you to both manually test the alarm and also silence false alarms. The alarm self-tests every 40 seconds and indicates any alarm faults with red LED warnings. It is ideal for domestic use with a high performance optical chamber which is best for slow smouldering fires.