How do you find a leaking pipe that is inside of concrete? A moisture meter won’t work, since there is no way for you to penetrate the concrete with the needle to test it. A cheap thermal imaging tool won’t be able to detect it either, instead you need to use a thermal imaging camera that has a higher than normal resolution and sensitivity.
It is also helpful to have a camera that can overlay the thermal image on top of an actual picture of the area, giving you the opportunity to pinpoint exactly where the problem lies.
The ability to detect a leak underneath a concrete floor will depend on many factors. One would be the temperature difference between the water and the floor. It is beneficial to make sure that the difference is as great as possible which might require changing the temperature in the building or running the water that is suspected to be causing a leak. Another is the depth below the surface at which the problem is located.
The upside to using thermal imaging is that you avoid having to rip up large sections of flooring when all that is needed could be a small area.