Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A voltage detector is a sensor used to detect the presence of electricity in a wire.The simplest type is a light bulb, or neon lamp and resistor, placed in series with the power supply or mains electricity. There are two bare metal probe s used to touch the two sides, as a volt-ohm meter would be used. These are typically produced in low-voltage (up to 50 volts) and line-voltage versions, and will work on AC or DC.Another type is often built into a small screwdriver, using a small LED or neon bulb and a low-ohm resistor inside the transparent plastic handle.