The Amprobe BT-120 breaker finder works on energized systems and are designed to quickly and easily indentify breakers in residential and commercial environments. Automatic sensitivity adjustment removes ambiguity from the results of the tracing, and the receiver will clearly and quickly identify the breaker with sound and light. The BT120 Circuit Breaker Tracer works on all electrical systems from 90V to 120V AC so you can meet the latest code requirements.