And since fiber-optic cables are typically run right along with utility pipes--neither phone nor gas companies want to have their lines cut--it's easy to connect a fiber backbone to the gas pipes at the neighborhood level, and beam a signal the final few feet to each home.
More modern versions of the tool add in a laser beam projector, which allows builders to level out the device and "draw" a long line of light across a wall, indicating an exactly level surface.