A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors/Alarms are usually housed in plastic enclosures, typically shaped like a disk about 150 millimetres (6 in) in diameter and 25 millimetres (1 in) thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization). Detectors may use one or both sensing methods. Sensitive alarms can be used to detect and deter smoking in banned areas. Smoke detectors in large commercial and industrial buildings are usually connected to a central fire alarm system.
Smoke detector mounted on a ceiling
Optical smoke detector with the cover removed; the angled plastic in an arc across the top is a light baffle
Inside a basic ionization smoke detector. The black, round structure at the right is the ionization chamber. The white, round structure at the upper left is the piezoelectric horn that produces the alarm sound.
An americium container from a smoke detector
Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires, but may also be used for pest control (fumigation), communication, defensive and offensive capabilities in the military, cooking, or smoking. It is used in rituals where incense, sage, or resin is burned to produce a smell for spiritual or magical purposes. It can also be a flavoring agent and preservative.
Smoke from a fire
Smoke from a bee smoker, used in beekeeping
Chemical composition distribution of volatile organic compounds released in smoke from a variety of solid fuels
Volatility distribution of volatile organic compound emissions in wood smoke