Finding an underground utility line is similar to tuning into a radio station. locator service or locator services each one transmits a different signal, and an underground service locator is meant to pick up signals that run through these lines. Many of them give off some type of electrical charge or radio signal. And like a radio station, most of them will have their own distinct charge or signal. However, some lines don’t give off a charge or transmit a radio signal of any kind. And in these situations, a transmitter can be used to run a signal through a metal line.