A compass or magnetometer by themselves can only detect/measure magnetic fields, and thus would normally only be able to detect ferrous metals and (possibly) some active electrical circuits in addition to the earth's magnetic field. That in itself can be useful at times. However, if you had a circuit with an induction coil on it (any size or shape), meant only to induce current in nearby metals, could you
a. Get a baseline measurement of the reaction of the compass or magnetometer to the induction circuit.
b. Move an assembly of the magnetometer/compass with the induction circuit around to
c. detect non-ferrous metals by the different reaction the compass/magnetometer has from its baseline when the induction circuit and sensors get near non-ferrous metals?