Patent ID: 7545254

Claim:
A method of protecting a motor vehicle (V), adapted for authorizing a starting of the vehicle only after a prior identification of a specific electronic tag (B) fitted with a transmitter/receiver circuit ( 6 ), situated inside a cabin of the motor vehicle, the method comprising the steps of: equipping the vehicle (V) with a central unit (UC) comprising a transmitter/receiver circuit associated with a plurality of antennas (INT 1 -INT 3 , EXT 1 -EXT 3 ) adapted for covering an entire volume of the cabin, and configuring the central unit (UC) and the electronic tag (B) to implement an authorization procedure such that the central unit (UC) instructs the transmission of an identification request signal, and upon receipt of the identification request signal at the electronic tag, the electronic tag (B) is configured to transmit, in response, an identification signal identifiable by the central unit, wherein, the vehicle (V) has antennas (INT 1 -INT 3 , EXT 1 -EXT 3 ) disposed and configured such that each zone of the cabin is covered by at least two of the antennas, the electronic tag (B) has means of three-dimensional measurement (A 1 -A 3 ) of an orientation of magnetic fields received by the electronic tag, and the central unit and the electronic tag are configured to perform an authorization procedure, the authorization procedure comprised of the steps of: determining a random sequence of emissions comprised of at least a first magnetic field emitted from a first of the antennas succeeded by a second magnetic field emitted from a second of the antennas, said first antenna and said second antenna determined randomly from the antennas (INT 1 -INT 3 , EXT 1 -EXT 3 ) of the vehicle (V), sending to the electronic tag (B) a signal representative of the randomly determined sequence of emissions, instructing the antennas (INT 1 -INT 3 , EXT 1 -EXT 3 ) to emit the succession of magnetic fields, forming the randomly determined sequence of emissions, upon receipt of the succession of magnetic fields by the electronic tag (B), measuring each of the magnetic fields to determine an orientation value representative of a resulting orientation of the electronic tag with respect to a source of emission of the magnetic field, thereby to establish a series of orientation values, each orientation value being representative of the resulting orientation, comparing the randomly determined sequence of emissions with the series of orientation values, and validating the authorization procedure upon determination of a correlation between the randomly determined sequence of emissions and the series of orientation values.