Patent ID: 7301438

Claim:
A method of ancillary protection against unauthorized use of an unpowered uniquely coded access and/or ignition key embedding an electronic identification periodic bit coding means connected to a secondary coil to be inserted in a receptacle or lock having electrically powered bit code sensing electronic means connected to a primary coil driven at a certain frequency, for transferring electric power to the said secondary coil in the access and/or ignition key, the method comprising the steps of: procuring and installing a device of directional emission of electromagnetic energy, positioning the antenna or directional emitter of the device at a certain distance from the position of said receptacle or lock, hiding or disguising its presence; irradiating toward said primary and secondary coils, respectively associated to said receptacle and to the key inserted therein an electromagnetic signal of the same working frequency of said coupled primary and secondary coils, amplitude modulated at a frequency randomly varying between a lower bound equal to the bit rate of the periodic bit coding and an upper bound equal to a multiple of the bit rate, equal or greater than the rate of said periodic bit coding and detectable by said sensing electronic means to corrupt the information content of said sensed code.