An EI Electronics Smoke Alarm with Silence Button feature which, when pressed, stops the annoyance of a nuisance alarm instantly , featuring an Ionisation sensor which enables it to react quickly to fast flaming fires. A loud alarm featuring a test button to enable regular checks. Battery operated. Ionisation smoke alarms operate on the principle that electrical current flowing between electrodes in an ionisation chamber is reduced when smoke particles enter. Loud alarm 85 decibels at 3 metres. No wiring required. Requires 1x 9V battery, included. Beeps if battery needs replacing. Always read instructions carefully.