US Patent 7164213 Theft prevention system for motor vehicles

For registering or updating the information of second identification codes stored in a theft prevention apparatus when the theft prevention apparatus is replaced, a third identification code sent from a third apparatus which is mounted in a motor vehicle is checked against a third identification code stored in the theft prevention apparatus, and must be identical thereto. Even if a third party prepares and installs an ignition key and a theft prevention apparatus of its own on the motor vehicle, the third identification code is not verified, and hence the information of second identification codes cannot be equalized.