Smoke Detector

A smoke detector is a device  that senses smoke, typically as an indicator of fire. Commercial security devices issue a signal to a fire alarm control panel as part of a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible or visual alarm from the detector itself.

Smoke detectors are typically housed in a disk-shaped plastic enclosure about 150 millimetres (6 in) in diameter and 25 millimetres (1 in) thick, but the shape can vary by manufacturer or product line. Most smoke detectors work either by optical detection (photoelectric) or by physical process (ionization), while others use both detection methods to increase sensitivity to smoke. Sensitive alarms can be used to detect, and thus deter, smoking in areas where it is banned. Smoke detectors in large commercial, industrial, and residential buildings are usually powered by a central fire alarm system, which is powered by the building power with a battery backup. However, in many single-family detached and smaller multiple family housings, a smoke alarm is often powered only by a single disposable battery.

Some smoke alarms use a carbon monoxide sensor or carbon dioxide sensor to detect characteristic products of combustion. However, some gas sensors react on levels that are dangerous for humans but not typical for a fire; these are therefore not generally sensitive or fast enough to be used as fire detectors.[citation needed] Other gas sensors are even able to warn about particulate-free fires (e. g. certain alcohol fires).

Obscuration is a unit of measurement that has become the standard definition of smoke detector sensitivity. Obscuration is the effect that smoke has on reducing sensor visibility; higher concentrations of smoke result in higher obscuration levels.

TUTORIAL LINK: Can be bought online or from any Electric appliances store.