Abstract: A battery immobilizer is described in which power provided by the battery to the ignition switch of an automobile is discontinued when the starter motor of the automobile is engaged without proper previous authorization. The authorization is provided by entry of a user code on a keypad within the automobile compartment. Once the code is entered, the automobile will start as normal, but if the code is not entered the battery will intelligently provide power to resistive loads while disconnecting power to the starter motor once the immobilizer detects that the starter motor has been engaged. The present battery can be connected to an automobile system using only standard electrical connections between the automobile electrical system and the battery and further does not require any connection between the immobilizer circuit and the user keypad.