Abstract: A sensing means is connected to the input of an electronic circuit for triggering a signalling means. The electronic circuit includes a continuous differential amplifier whose two inputs (-) and (+) are connected to the terminals of the sensing means. The input terminals are also connected by means of at least two switches to voltage sources in such a way that, by closing one of the switches, the polarity of the input terminal in question is reversed, to disable the detection device, and, by closing the other switch means, there is an increase, with the same sign, in the polarity of the input in question, for triggering the signalling means.

Abstract: The invention concerns an electromagnetic vibration-detector device, in particular for anti-theft, comprising a core which is displaceable in the interior of a winding, said core being secured to the free end of a vibrating blade which is rigidly secured at its other end, the device being characterized in that a thickness of cellular material is stuck on at least one of the faces of the blade, and the thickness of cellular material comprises on its free face a sheet of flexible material.