Very depending on the circumstances

I can only sum in an average rating for this product type for some reason it does not work on all walls equally well. So there are at my house (Bj. 1960) some walls where the equipment is very reliable and precise all power lines and water lines as well as other displays where the display of the device is almost useless.
Negative example: A wall (building outer wall) in front of my TV is displayed completely as red, often even with full magnitude of the fine and often display the signal, the power lines are laid. In this wall but are only two places actually power lines. I suspect that radiation from causing disturbance TV, but this was only in standby mode. Possibly also steel mats or steel grids are installed in the wall was, I know not (actually, the wall masonry, however, and should not contain mats), at least I have my holes drilled on "Good Luck" at the end.
Are also at walls where many lines (with me ever a wall in the bathroom and kitchen) has identify the device trouble uncritical areas. One must then pay close attention to the fine display, leave the sites many times in different directions, and completely ignore the red or yellow color ring Just basically, I have but then holes set can without it came to damages, but really uneasy It was not me. There were some areas in which I could make on the ads no rhyme.
In many other walls but the device works perfectly.