Temperature is measured through thermometers. Thermometers work using expansion and contraction. When the liquid inside the thermometer, mercury, gets hotter, it expands, rising up the tube. The same happens when the liquid gets cooler, it contracts, moving down the tube.

Many devices use temperature in their designs. These devices monitor the temperature around them or inside themselves to function properly. When a device registers the temperature to be too hot or too cold, it shuts off. One way it does this task is through the use of a bi-metalic strip. This strip of metal bends as it gets warmer. As it bends, it moves away from the magnet holding it to the complete circuit. When the connection between the strip and the metal is broken, the circuit is no longer complete, and therefore does not function. The power has been cut. Here is an example of a bi-metalic strip in a thermostat.

(look at the difference between the metal handles with the arrow)
connected bi-metallic strip
broken bi-metalic strip connection

Examples of this principle are: