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 breath alcohol level of a vehicle operator and prevents 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 includes first and second alcohol sensors. The second alcohol sensor is a backup for the first alcohol sensor and becomes operational if the first alcohol sensor malfunctions. The first or second alcohol sensors may be a mouth contamination sensor that distinguishes between mouth contaminants and alcohol contained within a deep lung breath sample. The system also includes sensors configured to detect impact (abuse) and vehicle motion.