How do ignition interlock devices work?

Arizona drivers who are convicted of drunk driving offenses may face the use of ignition interlock devices as part of their penalties along with the payment of fines, loss of driving privileges and even jail time. Many people have heard of IIDs but may not necessarily understand how they work. Having a working knowledge of this can be useful if facing a potential DUI conviction.

LifeSafer, an ignition interlock device manufacturer, provides useful details about the operation of most styles of IIDs in use today. They are comprised of two primary components. One of these components is a unit which measures the blood alcohol content of a driver by taking a breath sample. A driver must breathe into a tube that is connected to the device, which is commonly mounted on vehicle dashboards. 

The BAC data is sent to another component which is an electronic chip installed in the vehicle’s ignition system. If a driver’s BAC is below the legal limit, the chip unlocks the ignition, allowing the vehicle to be started and driven. If, however, a driver’s blood alcohol content is above the legal limit, the chip retains a lock on the ignition, preventing the driver from operating the vehicle until a subsequent test is passed. Even after a successful test and the starting of a vehicle, subsequent breath tests can be signaled while the vehicle is in motion. indicates that the National Highway Traffic Safety Administration and the Automotive Coalition for Traffic Safety have teamed up to test new versions of IIDs as a way to be more aggressive about preventing drunk driving. Both of the prototype systems would be built into new vehicles during manufacturing. One of the IIDs would leverage breath data but with a more streamlined, less invasive design that even eliminates tubes. The other new form of IID would measure BAC levels through touch-activated infrared sensors installed into steering wheels. It is not known exactly when or if these forms of ignition interlock devices would be adopted for use.

The use of IIDs is mandated by the court based upon a variety of factors. These include the presence of any prior drunk or drugged driving convictions on drivers’ records, whether or not minors were in vehicles being driven by arrested drivers and the specific recorded blood alcohol contents of drivers at the time of their arrests.