Abstract: An automatic theft prevention system for use in a vehicle powered by an engine that includes an ignition system operative from an ignition switch which is closed in order to run the engine and opened in order to stop the engine. The vehicle also includes a door for entry and a lid for gaining access to a portion of the vehicle, such as the trunk or hood. When the ignition switch is opened and a door to the vehicle is opened, the system automatically disables the ignition of the vehicle and enables an alarm system within two minutes after the door is closed. After the alarm system is enabled, an attempt to open the trunk or hood causes the alarm to sound instantaneously, whereas an attempt to open a door does not sound the alarm for a period of ten seconds. This feature enables the driver to gain entry to the vehicle and disarm the alarm system from the inside.