Abstract: A deactivatable coded marker for use in article surveillance systems has a core of soft magnetic material. An electrically conductive element at least partly surrounds the core, by reason of which the marker will generate a phase-shifted harmonic signal responsive to a reference signal. A magnetizable element of high coercivity is adjacent to and overlying the electrically conductive material, the marker generating the phase-shifted harmonic signal when the high coercivity element is not magnetized but generating a non-phase-shifted harmonic signal responsive to the reference signal when the high coercivity element is magnetized, whereby the high coercivity element neutralizes the effect of the electrically conductive element when magnetized. The deactivatable marker may have a plurality of cores, a plurality of electrically conductive elements and a plurality of separately magnetizable elements, forming respective and independently activatable and deactivatable marker parts.