Piezo switches and piezo buttons are special forms of pushbutton switches and pushbuttons. When pushed down manually a voltage is produced on the piezo principle; this voltage causes completion of a circuit. The switch status of most switches is shown by an LED indicator lamp. There are however also variants where when the switch is activated the operating surface sinks slightly into the surroundings, so that the switch status can be detected by feel. Piezo switches are available in various forms and colours. They are mostly made of aluminium or stainless steel. Since they contain no moveable mechanical parts, they are particularly tough with a long working life. Piezo switches and piezo buttons are therefore used in areas where damage by vandalism may occur, or where they are exposed to aggressive environmental effects. They are used for instance as controls in heavy industry, on public transport or on ships.