Ignition interlocks device or breath alcohol ignition interlock device (IID and BIID) are systems that test for alcohol on a driver's breath in his or her own car. An interlock includes a small alcohol sensor unit attached to the dashboard of the vehicle. Before the vehicle's motor can be started, the driver first must exhale into the device, if the resultant breath-alcohol concentration analyzed result is greater than the programmed blood alcohol concentration the device prevents the engine from being started.
In U.S almost all states have laws permitting the imposition of ignition-interlock devices as sentencing alternatives for drunken drivers. For example, In Georgia on being convicted for second DUI, the violator's license is suspended for no less than 18 months. During the final six months of this suspension the driver in question is required to have a working ignition interlock device installed in any vehicle that he or she intends to operate.
The following is an example of a state statute ( New York) defining Ignition interlock device:
Any blood alcohol concentration equivalence measuring device which connects to a motor vehicle ignition system and prevents a motor vehicle from being started without first determining through a deep lung breath sample that the operator's equivalent breath alcohol level does not exceed the calibrated setting on the device as required by section eleven hundred ninety-eight of this chapter.