A thermostat is a device that helps control the temperature in a room or building. It works by sensing the current temperature and adjusting the heating or cooling system to maintain a comfortable level. For example, when the temperature drops below a set point, the thermostat signals the furnace to turn on, warming the space. Modern thermostats can be programmable or smart, allowing users to set schedules or control them remotely through a smartphone app. This means you can adjust the temperature even when you're not home, making it easier to save energy and keep your living space cozy.