A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial,

industrial, and mass residential devices issue a signal to a fire alarm system,

 while household detectors, known as smoke alarms, generally issue a local audible or visual

alarm from the detector itself. Most smoke detectors work either by optical detection (photoelectric) or 

 detection methods to increase sensitivity to smoke. Sensitive alarms can be used to detect, and thus deter

smoking in areas where it is banned such as toilets and schools.

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