Abstract: The invention relates to monitoring techniques, such as angular movement monitoring techniques, in which an element with at least one peripheral irregularity is moved relative to a magnetic circuit so as to induce a variation in the reluctance in the magnetic circuit which can be detected externally. A device is disclosed including two magnetic elements defining respective magnetic circuits symmetrical with each other. Between the two magnetic members a gap is formed of approximately the same size of a peripheral irregularity, consisting of a notch or a tooth of a moving member, which is passed in front of the two magnetic circuits to cause a corresponding variation in reluctance in the magnetic circuits which produce a disturbance in the characteristics of symmetry, detectable by a sensor preferably a Wiegand-effect sensor.