Vehicle theft-prevention device

The present invention provides a vehicle theft-prevention device including a transponder associated with an ignition key, a disabling controller which outputs a predetermined rolling authorization code in response to a valid identification code received from the transponder, and an engine controller which permits an engine starting operation to continue when the rolling authorization code received from the disabling controller is valid, wherein the improvement includes a mechanism for storing a present rolling authorization code from the disabling controller as a previous rolling authorization code from the disabling controller and for storing a present rolling authorization code from the engine controller as a previous rolling authorization code from the engine controller when the present rolling authorization code from the disabling controller matches the present rolling authorization code from the engine controller, and a mechanism associated with the disabling controller for determining whether or not the previous rolling authorization code from the disabling controller and the previous rolling authorization code from the engine controller match when the present rolling authorization code from the disabling controller does not match the present rolling authorization code from the engine controller.