This is the probe for The Pro220K tone generator probe kit. It is designed to help contractors easily identify the termination point of any wire. Tone and probe technology has been around since the 1970's, but not like this. Advanced features including AC noise rejection, headlight, low battery light, combination metal/plastic tips, etc. make the Pro220K one of the most advanced tone/probe kits ever. Uniquely, the Pro220K uses AA batteries, providing tremendous battery life.