Abstract: The device comprises a magnet which induces several current pulses of alternating polarity in a primary winding, the current being restored in a resistance (R1) in series with a transistor (Ti). The voltage developed across the terminals of the resistance is applied to the input terminal (9) of a control circuit (7), via a capacitance (C), said control circuit (7) causing an interruption of the current generating an overvoltage. The capacitance (C) is charged by a first pulse, via a diode (D), connected in parallel with the transistor (Ti), and a resistance (10). The charge thus acquired remains active at the start of the subsequent principal pulse of opposite polarity, which follows, so that in the case of reverse operation of the engine, reversing the order of appearance of the pulses, no ignition takes place.