A familiar example of homeostatic regulation in a mechanical system is the action of a thermostat, a machine that regulates room temperature. At the centre of a thermostat is a bimetallic strip that responds to temperature changes. The strip expands under warmer conditions and contracts under cooler conditions to either disrupt or complete an electric circuit. When the room cools, the circuit is completed, the furnace switches on, and the temperature rises. At a preset level, perhaps 20 °C (68 °F), the circuit breaks, the furnace stops, and no additional heat is released into the room. Over time, the temperature slowly drops until the room cools enough to trigger the process again.