The Amprobe breaker finders work 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. Used to identify circuit breakers. Automatic sensitivity adjustment is easier to use and faster than the manual one. Microprocessor controlled design provides extremely accurate readings (always finds the right breaker). Durable and dependable. BT-120 works with standard 120V breakers. UL Listed. Environmental Conditions : For Indoor use, For Altitudes up to 2000 m, Pollution Degree 2. Transmitter Polarity : Automatic. Sensitivity Adjustment : Automatic. Users Manua