When you are trying to located the end of a wire behind a wall? We have'nt been successful locating an outdoor light switch box which is now behind a furred out stucco wall on a new 8 million dollar house. The original Electrical contractor Co. walked off the job and no as-built plans for where the other end of a 3-way light swich box is located. Supposedly on the OUTSIDE of one of the back doors. I guess so you could turn on the outdoor light to put your key in the door. Anyway, what are those electronic devices called that attach to the OTHER end of the circuit? thanks!