Yes the principal they operate on is just simple detection of a change in
the resonance or otherwise of a coil at a given frequency. Copper moves it
one way, iron the other way, and depending on how wide you make the window
shows its accuracy, if you narrow it too much you might miss it completely,
but too wide tends to give results that are vague to say the least as they
may detect changes due to more distant metal or indeed normal fluctuations
in the make up of the wall itself.


Its very much like a metal detector.
Some I have seen seem to be able to detect live wires, I suspect this is
done by detecting the AC field in some way.
Brian

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On 02/06/2019 21:58, Dave Liquorice wrote:
Any recomends/avoids?

The reviews of models that have a good overall rating still have a
significant number of bad ones. These don't obviously appear to be
from dimwits suffering from "operator error" or "bought a screwdriver
to drive in nails" categories.

Detection of cables/pipes mainly, studs would nice.

I have a cheap one and just recently used it to detect the nails holding
plaster board to the studding. Previously it was never much use but have
found if set properly it is quite useful. I use a known nail for example
and turn the wheel slowly until it beeps then pull the detector away and
it stops, place back over the nail and it should beep again.
I was too much on or off before without doing some fine tuning.