[G.R.]

Dane I think it is called a circuit toner, I looked at mine all it says is Radio Shack, no numbers or anything. It is a 2 piece tool, one end has a alligator clip you attach to an exposed wire or a pin probe you can push into a connected wire sheath this piece then emits a "tone", the "reader" picks up the tone and you can follow the wire to it's source, works ok but not more than 6'' away from the wire though--difference in quality between the RS version and the pro version. The sending unit uses two AA batteries and the reader uses a 9v.