[hyperific]

For anyone trying to find and map electrical wires in their walls I recommend an inductive electromagnetic listening device like the FarField on Tindie. Plug a device into an outlet and you'll be able to hear the electromagnetic field of the wire in your wall via the FarField's stereo inductors. Soma Ether is also a good one but pricey.

[mjlee]

Do you think you could trace copper pipes with the same technique?

[hyperific]

If there's current running through them then yes. There needs to be a EM field for the device's inductor to detect.