Thermostats are special gadgets that monitor the warmth in the premise with the help of sensors placed in different rooms. A predetermined value can be established as a desired heat level, and if this device detects that current temperature is different from the desired value it activates heaters or AC until desired environmental conditions are reached. Thermostat sensors may be presented as a collection of gadgets that differ by construction types and materials used.

There are three management principles used by these control devices - mechanical, pneumatic and electrical control. The first type reacts to various heat level changes by affecting mechanical parts and levers, and they are usually placed on or near the heater or cooling unit. The second type affects the HVAC/R system by a collection of tubes filled with air, that react to pressure changes (that occur due to variations in temperature). The third type thermostats have electrical wires that transfer signals from sensor elements to control panels of HVAC/R. Such thermostats can be presented in digital and analog forms.