What Is a Smoke Sensor?

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  • Written By: D. Grey
  • Edited By: Susan Barwick
  • Last Modified Date: 24 October 2019
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A smoke sensor is a device that has been specifically designed to detect smoke in the air and to alert any individuals nearby of its presence. Detectors generally serve as safety devices in both residential and commercial buildings in order to warn the residents that a fire may have started. Usually, a smoke sensor will detect smoke by using a photoelectric or ionization sensor, which activates a very loud sound from the unit itself. Industrial areas or large buildings will generally have multiple smoke sensors that are connected to a central fire alarm system. Proper maintenance of a smoke sensor is an imperative part of any fire safety plan, and may include testing the device and replacing batteries or other power sources when necessary.

There are two primary methods by which a smoke sensor is configured to detect smoke. A photoelectric sensor works by projecting a beam of light at a 90 degree angle into a tube, at the end of which is a light sensor. When smoke is in the air and enters this structure, there will be less light. This is detected by the sensor and causes the alarm system to activate.

A smoke sensor that uses an ionization sensor contains an ionization chamber, which is made up of two small plates that have an electric voltage in the air between them. If smoke enters the chamber, the air between these two plates becomes ionized and the current is. This prompts the alarm sound.


The National Fire Protection Association of the United States has published statistics indicating that deaths in residences are lowered by 45% when a smoke sensor is present in the home and working properly. Common causes of smoke sensor malfunction are drained battery power sources, improper set-up, such as incorrectly placed batteries, debris and other substances blocking or disrupting the the sensors, or simple part failure.

Most units allow users to test the audible or visual warning system by pushing a button. To test the sensor itself, however, most manufacturers generally recommend using canned smoke sensor aerosol. Using a common source of smoke such as a lit candle or cigarette is usually not recommended as the debris can clog the sensor, and prevent it from working in the event of an actual fire.


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