First alert, sealed battery operated, photoelectric smoke alarm, with escape light, premium smoke detection capabilities into a sleek, compact design, for those who want a reliable detection system, uses a photoelectric sensor to detect smoke from smoldering fires while keeping false alarms to a minimum, a patented smoke entry system allows for a direct path to the photoelectric smoke sensor, helping ensure reliable detection, comes equipped with an ultra bright led escape light, which helps illuminate an evacuation path during emergencies, takes up a fraction of the space of traditional smoke alarms, can be mounted unobtrusively on a wall or ceiling, a loud alarm sounds when smoke is detected, convenient test/silence button lets you easily check whether your alarm is functioning.