Abstract: A metal detector has a balanced coil arrangement fed by an audio frequency oscillator. In-phase and quadrature components arising when the arrangement is unbalanced by proximate conductive objects are detected, the sense of the quadrature component depending on whether the object is ferromagnetic or non-ferromagnetic. The quadrature component varies the frequency of another audio frequency oscillator above and below a mean value and the in-phase component controls the strength of the audio frequency signal fed from the second oscillator to a transducer such as headphones.