The only moisture meter
I have familiarity with the medium quality Tramex Skipper. This device sells for about $400, and has no prongs or wires, per se. It has a number of different scales for the type of surface (i.e., wood, cored fiberglass, solid fiberglass, etc.) you are testing and the meter is pressed to the surface to get a reading. Having said all this, the use of moisture meters is, IMHO, an artform and not science. Moisture meters frequently produce erratic or erroneous results when not calibrated accurately or used appropriately. For example, a moisture meter used to test the integrity of a foam rudder with a steel framework at its core will produce all sorts of readings unless you know exactly and precisely where the framework is -- and avoid it. As such, the use of moisture meters by trained professionals may provide more useful information than that obtained by a novice on the same boat.