Which device operates with a bi-metallic strip and detects heat?

• A. Heat detector
• B. Smoke detector
• C. Carbon monoxide detector
• D. Gas detector

Answer: (A)

Bi-metallic strips bend when temperature changes because the two metals expand at different rates. In a heat detector, this bending acts as a switch: when the temperature reaches a preset level, the strip moves and completes an electrical circuit to trigger the alarm. That mechanical response to heat is the defining feature of heat detectors, so a device that operates with a bi-metallic strip to detect heat is a heat detector.

Smoke detectors, carbon monoxide detectors, and gas detectors use completely different sensing principles—smoke detectors look for smoke particles with light or ionization methods, CO detectors use chemical sensors to detect carbon monoxide, and gas detectors rely on sensors designed for various gases.