What type of fire detection system activates an alarm when the temperature of the space reaches a predetermined level?

A fixed temperature heat detector is designed to activate an alarm when the ambient temperature reaches a specific, predetermined level. These detectors are calibrated to respond to heat, and once the temperature exceeds a certain threshold, usually set based on safety standards and the environment in which the detector is installed, they will trigger the alarm system. This type of technology is beneficial in settings where smoke or flames might not be present initially but where a rise in temperature can indicate the start of a fire.

In contrast, smoke detectors work by sensing smoke particles in the air and activating the alarm prior to significant heat development, while rate-of-rise heat detectors trigger alarms based on the speed at which the temperature increases rather than a set temperature threshold. Flame detectors, on the other hand, are designed to respond specifically to the infrared or ultraviolet radiation emitted by flames. Thus, the fixed temperature heat detector's reliance on a specific temperature level is what distinguishes it as the correct choice for this question.