Compact Size AC/DC Low Voltage Detector (5 to 50V AC/DC) The Extech ET23B Compact Size AC/DC Low Voltage Detector (5 to 50V AC/DC) is a main unit with a voltage detection range of 5 to 50V AC/DC. The ET23B features a neon light Voltage indicator and has built-in test lead clips, a pocket clip, and insulated housing.