If I was in the same situation I would probably try one of three things. You might be able to achieve your goal with a standard hobby type metal detector, assuming you have rebar or steel mesh placed in your concrete slab. The mesh or rebar is usually placed towards the bottom of the slab, so it should be located deeper under the concrete surface in a place where the slab is thicker. If you adjust a metal detector so that it lightly beeps when moved over the top of the metal mesh where you know the concrete is thin you might be able to hear that beeping sound disappear or lessen noticeably when you go over an area of the floor where the steel is located an inch or more deeper down in the concrete.
An alternative solution might be to use water. Wet the surface of your slab as equally as possible all over and watch it closely as it dries to see if a certain square or rectangular section of the floor either dries more slowly or more quickly than the rest of the slab. Basically, it's a poor man's version of a thermal camera, because the water will evaporate a tiny bit slower in an area that's a little bit colder than the rest of the slab. This technique probably wouldn't work if you have any sort of epoxy or a similar coating on your slab.
Lastly, rent or purchase a rebar locator. It is a tool that works just like a stud finder, but it can be used to find rebar in concrete instead. They often also give you an approximate depth of the rebar in the concrete as well, so you would look for an area of the floor where the rebar is deeper down in the slab.
Something similar to this-
https://www.amazon.com/Zircon-Metal...-Detector/dp/B09DZ5W3R5/?tag=atomicindus08-20
