Room thermostats regulate and maintain a desired setpoint temperature throughout a residential or commercial space to keep occupants comfortable. They sense the temperature of the air and switch the heating or cooling system on or off as the temperature varies. Also known as wall thermostats, they typically mount on an interior wall, but some plug into a wall outlet. Line-voltage thermostats regulate the temperatures of HVAC systems that require direct electrical power, like electric baseboard heaters, attic fans, and fan coil units. Low-voltage thermostats control temperatures of whole-building HVAC systems. They send a signal to the heating or cooling system's control board to operate it instead of powering it directly. Thermostat accessories protect, mount, and enhance the functionality of room thermostats.