A specialized type of gas-filled tube called a Gas Discharge Tube (GDT) is fabricated for use as surge protectors, to limit voltage surges in electrical and electronic circuits. Due to their very low capacitance, gas discharge tubes are commonly used on high frequency lines, like in telecommunications equipment. They can also be used in industrial and consumer electronics, such as in surge protectors and alarm systems. Other applications include instrumentation circuits, power supplies and medical electronics.