Do not get me started. I had a customer that bought one of these "testers" it was a homebrew box with some meter on it. Since it had no brand name no telling what it was calibrated to. She claimed her girl was exposed to excess EMF and cause her ADD. As she scanned the wall behind her bed the meter peaked (a 1" copper water line was in the wall) She wanted to know what to do. I suggested she move her bed to the other wall but she said it would upset the decorating style of the room. At that point I suggested she call a plumber to move the pipe at a great expense. She did not like that ether. Go figure.