Which heat detector utilizes two metals that expand at different rates to function?

The bimetallic detector operates on the principle of thermal expansion, utilizing two different types of metals that expand at different rates when exposed to heat. As the temperature increases, one metal expands more than the other, resulting in bending or movement. This mechanical movement triggers a switch that activates an alarm or sends a signal, indicating an increase in temperature that could suggest a fire. This method of detecting heat is reliable since it responds directly to temperature changes.

In contrast, ionization smoke detectors rely on radioactive material to detect smoke particles, while photoelectric sensors work by detecting light changes caused by smoke entering the detection chamber. Heat-sensitive cables function by changing resistance based on temperature changes, which is a different mechanism from the physical bending of bimetallic strips. Understanding these distinctions highlights the unique operation of the bimetallic detector among the listed options, making it the correct choice for this question.