Abstract: An electronic theft-alerting system, including magnetometers, such as multiaxis magnetometers, arranged in respective stations and configured to output respective vector signals representing movement of respective magnetic field vectors; and a signal processor coupled to receive the first and second vector signals, and configured to detect a corresponding movement of a first magnetic field vector and a second magnetic field vector. Detecting commencement and continuance of fluctuation the first magnetic field vector, determining whether to raise or forgo to raise an alarm that warns about a possible theft-related event in response to the determining of commencement and continuance of fluctuation of the first magnetic field vector or the second magnetic field vector.

Abstract: A method of detecting a metal object in a detection zone between a transmitting antenna (101) and a receiving antenna (102) installed in proximity of a revolving door (110), the method comprising: in real time: demodulating a signal received via the receiving antenna (102) to provide a first signal (y; 501); filtering the first signal (y; 501) by a first adaptive notch filter (201) to suppress at least a fundamental tone or a fundamental tone and one or more harmonic tones of the fundamental tone in a filtered signal (e; 502); and processing the filtered signal (e; 502) to detect an impulse (504), and while the impulse develops, computing a feature value of the impulse and determining whether the feature value exceeds a threshold. In case the feature value exceeds the threshold, setting a first alarm detector. In this way a so-called booster bag can be reliably detected the moment it passes the detection zone.

Abstract: A tag-based electronic theft-preventing system further comprises a first and second multi-axis magnetometer arranged at the two sides of an entrance to a shopping area and configured to output a first and second vector signal representing movement of a first and second magnetic field vector, respectively. A signal processor estimates a first rotation of the first magnetic field vector and a second rotation of the second magnetic field vector, and generates an indicator signal comprising indication of a counter-direction rotation or a same-direction rotation. The system computes therefrom if an unlock magnet for an anti-shoplifting tag is entering the shopping area and determines whether to warn about a possible theft-related event. Other indicators contemplated in the processing are for instance vector magnitude, continuity of detection, duration of detection, change in electric field.