A detectable component has a first inductive coupler (L;M) adapted to couple inductively to a second inductive coupler (L1) of a detection apparatus when the detectable component is in range of or coupled to the detection apparatus. The first inductive coupler has a resistive component (M) with a resistance that varies with magnetic field to cause modulation of a carrier signal supplied to the second inductive coupler of the detection apparatus, the detectable component having a characteristic signature that enables the detectable component to be distinguished by the detection apparatus from other such detectable components having different characteristic signatures.