Abstract: The present invention provides an antitheft system comprising a pair of spaced coils which are excited to produce an alternating magnetic field within a surveillance zone between the coils. Thus, a magnetic marker having a permeability of less than 150,000 and a coercive force of substantially 2.5 MA/CM which is carried through the surveillance zone cuts or links lines of magnetic flux within the zone regardless of the orientation of the marker. Electronic circuitry detects the electromagnetic field within the zone at harmonic frequencies greater than the frequency of the oscillating magnetic field and, through coherent correlation, determines the presence of the marker within the surveillance zone as well as distinguishing and differentiating the marker from other ferromagnetic materials.

Abstract: An electronic security system to detect the presence of an object which has had a label affixed thereto when said object passes through a surveillance zone comprising an oscillatory electromagnetic interrogation field having three separate and distinct vector components produced by driving the transmitting coils located in housings on either side of said surveillance zone with an alternating power source repetitively in and out of phase with respect to one another so as to form magnetic lines of flux having one vector component in the in-phase mode and two vector components in the out-of-phase mode. The signals generated by the label are received by coils in said housing and are processed by electronic circuitry adapted to distinguish said label signals from spurious signals with a high degree of accuracy. The label can be deactivated so as to pass through the surveillance zone without triggering a system response.