Fixed-temperature heat detectors activate when what condition is met?

• A. Ambient humidity reaches threshold
• B. Ambient temperature reaches the detector's preset point
• C. Temperature difference between two sensors
• D. Motion is detected

Answer: (B)

Fixed-temperature heat detectors activate when ambient temperature reaches the detector’s preset point. The device uses a heat-sensitive element that holds its switch in a normal state until that specific temperature is reached, at which moment the contacts change and the alarm is triggered. This gives a definite temperature threshold as the trigger, rather than relying on how fast the temperature rises. They aren’t activated by humidity or motion, and they don’t rely on comparing temperatures between two sensors—that describes other types of heat detectors that use differential or rate-of-rise sensing. If the environment never hits the preset temperature, the detector won’t activate, whereas rate-of-rise detectors would respond to rapid temperature increases even if a fixed point isn’t reached.