Wait, by using a moisture meter with pins it becomes an invasive inspection, then we go down the slippery slope?? I don't get it. I remove covers, panels, pull up carpeting in corners, etc, etc to do what's needed for thorough inspection. We could start the drop ceiling tile discussion again. A moisture meter is an instrument that should be used with great care and thought. Is the subsurface material that you are scanning drywall or plaster? Minimal thought. Walk into room, look at wall, tap on it if necessary, and you should know exactly what it is.