DUI Laws, DUI Penalties, and DUI Defense What is an ignition interlock device? Copyright 2010 All rights reserved http://www.duilawsintennessee.com An ignition interlock is a sophisticated system that tests for alcohol on a driver's breath. It is a device that requires a vehicle operator to blow into a small handheld alcohol sensor unit that is attached to a vehicle's dashboard. The car cannot be started if a BAC is above a preset level (usually .02 to .04 BAC). Alcohol safety interlocks that meet the standards issued by NHTSA (see the See NHTSA Conforming Products List and Technical Information Regarding Alcohol and Drug Law Enforcement Technology) not only require a test to start the engine, but also require a test every few minutes while driving. Called the "rolling or running retest," it prevents a friend from starting the car and then allowing an impaired driver from taking over the wheel (NHTSA guidelines call for only one subsequent test and the Alberta, Canada standard calls for multiple running retests). With modern safeguards, alcohol safety interlocks are extremely difficult to circumvent when properly installed and monitored every 30 to 60 days.