This Brennenstuhl BR 8221 Extra Longlife Smoke Alarm is a photoelectric detector that is tested in accordance with EN 14604. With an impressive 10 year operational life (without changing a battery) you dont have to worry about constantly testing & replacing the batteries. The unit comes complete with a 3V lithium battery for constant operational readiness & it is automatically activated on the commissioning of the alarm. There is a clear & concise optical function display with a test button for functional testing. A mute function is also included.