A thermostat is what?

• A. A temperature-actuated switch.
• B. A humidity sensor.
• C. A device that controls lighting.
• D. A device that stores temperature data.

Answer: (A)

A thermostat is a temperature-actuated switch. It senses the ambient temperature and, when the temperature reaches the setpoint, it opens or closes an electrical circuit to turn heating or cooling equipment on or off. This switching action is what maintains the desired temperature in a space. Modern thermostats may include digital displays, programmable features, or data logging, but the essential function is to respond to temperature with a control action that starts or stops the equipment. The other descriptions describe different devices—humidity sensing, lighting control, or data storage—not the core role of a thermostat in regulating temperature.