A method for defeating a two-thief attack on a passive RKE system by using frequency hopping. Radio frequency signals are transmitted between a fob and a vehicle. The transmitted signals hop between at least two radio frequency transmitting channels in a particular pseudo-random pattern known to the vehicle. At the vehicle, the transmitted signals are received in a process that is sequentially adjusted to take account of the known characteristics of each portion of the known pattern. Anomalies in the pattern of the received signals are detected and, if the anomalies exceed permissible limits, access to said vehicle is blocked.