This multimeter Bosch works well. it detects the problem without son, iron bars and harder beams.

Usually this kind of machine works poorly or not at all. But Boch multimeter detects almost all with no problems: electrical son, iron bar, metal .... (I tested in places where I knew there were things).
As for the wooden beams (which is much more difficult), this machine gets there but there are false positives. You have to go several times to confirm the detection. I tested through the "bacula" and it detected all the beams, plus some other imaginary (probably nails!) I struck with a small drill.
So efficient and secure machine to recommend despite the high price.