A method for enabling an apparatus (15) to operate only after detecting with receiver elements (11) located proximate to the apparatus, a signal transmitted by portable transmitted elements (1), which consists in no longer taking into account detection by the receiver means (11) of the signal transmitted by the transmitting elements (1), after activating presence sensing elements (22) provided proximate to the apparatus, or integrated in the apparatus. Once activated, the presence sensing elements (22) neutralize the transmitter/receiver device (1, 11) and the apparatus can operate normally without being perturbed by possible statics or accidental losses of signal. The inventive method and device are applicable to an antitheft safety device for a motor vehicle.