Fire alarm notification appliance

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A Wheelock MT-24-LSM fire alarm horn and strobe.

Fire Protection


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A fire alarm notification appliance is an active fire protection item. It is an electromechanical or electronic bell, klaxon, chime, horn, buzzer, speaker, strobe light, or other device that warns people in a building of a possible fire or other condition requiring emergency evacuation. Some horns can produce several different kinds of sounds, including the Code-3 temporal pattern (0.5 second pulse, 0.5 second pause, 0.5 second pulse, 0.5 second pause, 0.5 second pulse, 1.5 second pause), which was designed to be a distinct pattern used only for evacuation purposes. Other sound patterns include march time (0.25 second pulse, 0.25 second pause, repeat), a continuous tone, hi-lo (0.25 seconds alternating between two tones of differing frequency), siren (up-and-down sweep in frequency), slow-whoop (slow rising sweep upwards in frequency), and an electronic bell sound. Fire alarms are often very loud, sounding at between 90 and 100 decibels [1]. Firefighters have been known to have hearing problems after exposure to alarms over many years. Typically, when a fire alarm is sounded, emergency responders are summoned, the building is evacuated, people gather at predetermined assembly points, and a roll call is held.

In the United States, with the advent of the Americans with Disabilities Act of 1990, fire alarm systems changed dramatically. Along with an audible alarm, fire alarm notification appliances now have strobe lights to alert the hearing impaired. However, some fire alarm notification appliances have had incadescent lights on them since the 1970s, usually as separate light plates installed onto the existing horns or bells.

Also, in the event of a total power failure due to the fire, these strobe lights can assist building occupants in finding their way to the nearest exit by illuminating the corridors, since all modern fire alarm systems have backup power systems in place.

Strobes are required to be synchronized in situations where a person would otherwise be exposed to more than two flashes per second. This prevents random flashing, which could cause those with photosensitive epilepsy to have an epileptic seizure.