An EI Electronics Smoke Alarm, featuring an Ionisation sensor which enables it to react particularly effectively to fast flaming fires. A loud alarm featuring a test button to enable regular checks. Battery operated for protection even in the event of a power cut. Ionisation smoke alarms operate on the principle that electrical current flowing between electrodes in an ionisation chamber is reduced when smoke particles enter. Battery included. Loud alarm 85decibels at 3 metres. No wiring required. Requires 1x 9V battery, included. Always read instructions.