An ignition interlock device is an in-car alcohol breath screening device that prevents a vehicle from starting if it detects a blood alcohol concentration (BAC) over a pre-set limit of .02 (i.e., 20 mg of alcohol per 100 ml of blood). The device is inside the vehicle, near the driver's seat, and is connected to the engine's ignition system. Many states need that the device be used by those convicted of DUI.