Abstract: A vehicle theft prevention device prohibiting release of a vehicle theft prevention control under a predetermined condition even when the control is applied using an authorized portable tool to thereby prevent the vehicle from running. Even when a vehicle ECU 14 controls to release theft prevention control applied by a theft prevention device including an engine control device 12a, a steering locking device 12b, and so on based on a specific code corresponding to a request code from an authorized portable tool 16, the specific code corresponding to the request code from the first portable tool 16 is invalidated upon receipt of a security request code. With this arrangement, an operation to release the theft prevention function of the theft prevention device is prohibited. Moreover, when release control is performed based another specific code (a security code) requiring a request code, vehicle theft can be prevented.

Abstract: An electronic instrument having a resettable security code as a way of preventing the burglary of the electronic instrument mounted to a movable device such as a car. When the electronic instrument is mounted to the movable device or a battery is exchanged, the entry of the security code is required by the user. If the user does not know or remember the security code, a random number is automatically generated inside of the electronic instrument and converted into an initializing code according to the predetermined rules. The user reports the generated random number to a service company or the manufacturer. The service company or the manufacturer checks if the user is registered. When the user is certified, the service company or the manufacturer gives the initializing code corresponding to the random number to the user. Then, the user enters the given initializing code for resetting the security code.