But the fact that the brass reacts more to temperature than iron does enables the switch to open and close in response to temperature. As your house gets cold, the brass side contracts more than the iron pulling the strip toward the brass side. If the strip bends far enough, it touches an electrical contact, completing the circuit, and turning on the heater. As the house warms up, the brass expands, pushing the strip away from the electrical contact and shutting off the heat. Finding The Metal Strip Some thermostats don’t use the two part metal strip. And if your’s is one of these, you probably have just such a strip somewhere else. Perhaps in your oven thermometer, your electric toaster, or the automatic choke on your car.