A vehicle ignition interlock system includes a breath analyzer and a controller operably connected to the breath analyzer and to an ignition system of the vehicle. The breath analyzer detects the breath alcohol level of a vehicle operator and is configured to prevent vehicle ignition if a breath alcohol level is greater than or equal to a threshold value. The controller requires the vehicle operator to periodically take breath analyzer "retests" after vehicle ignition in order to allow vehicle operation to continue. The breath analyzer also detects the presence of alcohol within the vehicle, such as alcohol emanating from an open container of alcohol. The controller may override one or more periodic retests if alcohol is not detected within the vehicle over a predetermined period of time. In addition, the controller may increase the frequency of periodic retests of the vehicle operator in response to detecting alcohol within the vehicle.