A thermostat is a device that regulates the temperature of a heating or cooling system so that it maintains a desired temperature. It is a control unit that senses the temperature and compares it to the desired temperature setting. If the temperature is too high or too low, the thermostat sends a signal to the heating or cooling system to turn on or off. Most modern thermostats require a common wire for power. Dummy thermostats can also be used to trick building occupants into feeling more comfortable and in control. It is important to maintain and check the accuracy of the thermostat to ensure it is working properly.