Detection apparatus and detectable component

A detection system comprises a detection apparatus (2) for detecting relative movement of a magnetic element detectable component (3). The apparatus comprises an oscillator coupled to a detection component which has an impedance that varies with magnetic field when an oscillating signal is applied to it. The detection component may exhibit giant magneto impedance (GMI). A sensor detects impedance variations of the detection component resulting from movement of the magnetic element (3) relative to the detection apparatus (2) and an output indicates such impedance changes. The detection system may be used in a toy or game, in a flowmeter, level indicator, or for tagging applications where relative movement is to be sensed.