Smoke Detector

A smoke detector is a device that senses smoke, typically as an indicator of fire, usually housed in a disk shaped plastic enclosure roughly 125 millimeters across, and it detects smoke either optically, by a photoelectric method, or by a physical ionization process, with some detectors using both. Household smoke detectors, also called smoke alarms, sound an audible or visual alarm and may be interlinked so that any one unit detecting smoke triggers every connected unit, powered by a battery, by mains electricity, or by a combination of the two so a battery can back up the mains supply. Commercial smoke detectors typically send a signal to a fire alarm control panel as part of a larger fire alarm system rather than sounding an alarm on their own. According to the United States National Fire Protection Association, the risk of dying in a home fire is roughly cut in half in houses with working smoke detectors, which recorded 0.53 deaths per 100 fires compared with 1.18 deaths per 100 fires without them, in data covering 2009 to 2013.