Plug the circuit breaker detective's transmitter into the circuit you want to find, go to the breaker box and the receiver identifies the correct breaker. The unit features a flashing arrow indicator and digital calibration for faster, easier and more reliable performance. The auto shutoff feature saves battery life. - Flashing arrow indicator for easier identification - Digital calibration for faster, easier, more reliable identification - Fully automatic - Manual and automatic shutoff ** Requires 9 volt battery, sold separately.