Quickly locate the right 120v circuit breaker or fuse, without guessing! When you need to turn off a 120v circuit breaker or remove a fuse, you won't have to yell upstairs, "Is it off yet?" several times. Simply plug the UL-listed transmitter into an outlet on the circuit you want to locate. Go to your panel and run the receiver's tip over the breakers or fuse rows until the arrow illuminates and the speaker beeps. So easy - everyone should have one in their toolbox!