What type of detector activates at a preset temperature level when its components melt?

A fixed temperature detector is designed to activate when the temperature reaches a specific preset level that causes its components to melt. This mechanism is crucial for detecting fires in environments where rapid temperature changes are less common, as it provides a reliable method for alerting occupants of a potential fire hazard.

In contrast, other types of detectors function differently. A rate of rise heat detector responds to a rapid increase in temperature within a certain period, rather than activating at a specific predetermined temperature. Ionization smoke detectors and photoelectric smoke detectors focus on detecting smoke particles rather than temperature changes. This distinction clarifies why the fixed temperature detector is the appropriate choice for the question regarding activation at a predetermined temperature threshold.