I need a way of tracing wires inside exterior walls and celings.
The walls have timber frames wih plasterboard (i.e. with a cardboard
surface and a gypsum core) on the inside, polystyrene foam insulation,
building paper and weatherboards.

I do have a stud finder but that is useless on exterior walls because
the outside of the plasterboard has aluminium foil on it, and the
wires are beyond that. The stud finder emits a continuous beep within
a foot of all the outside walls.

A radio tuned off station works well but not where there is foil.

If I buy some device there is no guarantee that it will work past the
foil.

Maybe I could use a solenoid connected to headphones.