Patent ID: 7443286

Claim:
An anti-theft system for a vehicle, comprising: an on-vehicle unit including reporting means configured to report, by radio, an illegal activity affecting a vehicle with ID information of the vehicle or a user of the vehicle to a center in a case where the illegal activity to the vehicle is detected; and an external facility provided at a site where the vehicle having the on-vehicle unit is located, the external facility including: ID information obtaining means configured to obtain ID information of the vehicle located at the site or of a user of the vehicle; obstruction radio wave detection means configured to detect a radio wave obstructing the radio report by the reporting means; and illegal activity prevention means configured to report the existence of the obstructing radio wave with ID information obtained by the ID information obtaining means to the center by using a frequency different from a frequency used for the radio report by the radio reporting means as an action to prevent the illegal activity in a case where the obstructing radio wave is detected by the obstruction radio wave detection means.