METHOD TO PREVENT UNAUTHORIZED USE OF VEHICLE Russian patent published in 2003 - IPC

FIELD: transport engineering; security systems. SUBSTANCE: transponder with individual code is given to user. When generating enquiry by pseudorandom code on vehicle, expected code of answer is determined and remembered, calculated check sum is added to code of enquiry and signal is transmitted on the air. If transponder is in covered zone, check sum is calculated by enquiry code and if sum coincides with adopted one, user's character code and answer code corresponding to enquiry code are included into answer signal which is transmitted on the air. Signal is received in vehicle and answer code is distinguished and compared with expected code, and if they coincide, service settings are carried out. Difference is that calculation of answer code in transponder is started directed directly at termination of reception of enquiry code, and transmission of answer is started immediately after revealing of coincidence of adopted and calculated check sums. Directly after termination of transmission of enquiry, readout of reception time is started during which presence of radio signal with enquiry and answer signal carriers is traced. If radio signal fades out in course of time of reception, further reception of answer is prohibited till the next enquiry signal. EFFECT: improved efficiency of protection. 3 cl, 1 dwg