Smoke Detector


Smoke Detector


The smoke detector on a fire alarm system is the associated attached devices that is designed to detect the presence of smoke and fire. A commercial, residential and industrial smoke detector will transmit data to the fire control panel indicating the presence of heat, smoke and fire. Smoke detectors are housed in a round disk shaped plastic enclosure about 1 inch thickness and 6 inch diameter. A smoke detection device operates as optical detection (photoelectric) or physical process (ionization) and in some cases both to increase sensitivity.


Commercial, residential and industrial fire detectors are powered by the fire alarm control panel with attached power supplies. If the fire alarm loses power, the backup battery will continue to power the device and activate an alarm. If you have a smoke detector installed in your home, chances are the device operates by a single disposable battery.

Optical Smoke Detector

The optical smoke detector is designed with a simple light sensor. In the absence of smoke, the light passes in front of the detector in a straight line. If smoke enters the optical detector chamber when crossing the beam of light, it scatters the smoke particles directing in towards the sensor and thus activating the fire system.


Optical smoke detectors are quick in detecting smoke particles originating from smoldering coal and fires. Independent test indicate that an optical detector detects particles in smoke from a fire 30 times slower than the ionization smoke detector.

Ionization Smoke Detector

A ionization detector is less expensive than the optical detector but is not widely used because it is more false alarm prone when compared to the performance of a photoelectric smoke detector. A ionization smoke detector detects particles in smoke that are to small to be visible with the naked eye. It operates with a small radioactive americium that passes thru an ionization chamber filled with air space between two electrodes and permits the small constant current between them. Smoke will enter the chamber and absorb the alpha particle, thus reducing the ionization, interrupting the current and activating the fire alarm system.

Carbon Monoxide Smoke Detector

In some cases, a fire alarm smoke detector may use a carbon dioxide sensor to detect high levels of dangerous carbon monoxide from combustion. It is important to note that NOT every detector is designed to warn of poisonous levels of gases in the absence of an actual fire. Learn the operational and cost differences between optical, ionization and carbon monoxide smoke detectors.