Start with the meter. Turn off every fixture, including the ice maker line if you can, and watch the small dial or the leak indicator. If it moves, water is leaving the system somewhere.
The usual innocent causes are a toilet fill valve and an irrigation valve. A plumber rules those out before calling it a slab leak. Toilets that run are cheap compared with cutting a floor, and they waste a surprising amount of water.
If the fixtures are dry and the meter still moves, the next step is listening. Acoustic gear on the slab, the walls, and the hose bibs narrows the run. A hot spot means the hot side. No hot spot does not mean there is no leak.
Detection on a house typically runs $250-$700. The repair is a second number, written after the spot is marked. Pipe Pro SD matches you to a plumber who can separate those two steps. We do not sell a detection that only exists to justify a repipe.