An anti-theft system for a vehicle includes parking location sensing means for sensing a present parking location of the vehicle, user location sensing means for sensing a present location of a user of the vehicle, distance calculating means for calculating a distance between the present parking location of the vehicle and the present location of the user of the vehicle, and security level setting means for setting a security level of the anti-theft system based on the distance between the present parking location of the vehicle and the present location of the user of the vehicle.