A capacitance switch needs only one electrode to function. The electrode can be placed behind a non-conductive panel such as wood, glass, or plastic. The switch works using body capacitance, a property of the human body that gives it great electrical characteristics. The switch keeps charging and discharging its metal exterior to detect changes in capacitance. When a person touches it, their body increases the capacitance and triggers the switch.
Capacitance switches are available commercially as integrated circuits from a number of manufacturers. These devices can also be used as a short-range proximity sensor.