How Do Heat Alarms Work?

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 135 degrees F). 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.