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How Do Heat Alarms Work?

Updated April 17, 2017

Heat alarms are devices that may be installed in addition to smoke detectors. Rather than detecting particles in the air (as smoke detectors do), they activate as a result of high temperatures.

Rate of Rise Detectors

Some heat detectors trigger only as a result of a rapid rise in temperature. They contain a thermometer that triggers an alarm in reaction to a rapid rise in temperature.

Fixed Temperature Detectors

Fixed temperature detectors react when the air around them reaches a certain temperature (they are usually set to 57.2 degrees C). They contain a thermometer that triggers the alarm when it reaches that temperature.

How They Work

Many detectors contain a small piece of metal that changes in size in response to air temperature. Higher temperatures cause it to extend, eventually bringing it into contact with another piece of metal completing a circuit and triggering the alarm.

Combination Detectors

Many detectors contain both rate of rise and fixed temperature sensors to increase their chances of accurately and quickly responding to a fire.

Electronic Detectors

Some modern detectors contain small electronic sensors which measure the air temperature and trigger a system when it reaches a certain point.

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About the Author

Abe Robinson has been a freelance writer since he graduated from college in spring 2009. He has written for a variety of websites and has provided content for the University of Chicago's "Ceremonial Words – Ritual Acts." He also holds a Bachelor of Arts degree from that university, receiving honors for his B.A. Thesis "Anglo-American Perceptions of Japanese Imperialism in Taiwan."