Automatic bathroom faucets have battery operated or electrically powered sensors that detect motion near the faucets and trigger the water to flow. The sensors could be found either at the base of the faucet or on its head. Some sensors have the capability to change the temperature of the water. You merely sway your hand at the left side of the sensor to make the water warmer. If the temperature of the water is warm, you pass your hand at the right side to activate a cooler water flow.