Q: How does an ignition-interlock device work?

A: Essentially, an ignition-interlock device is a “breathalyzer on wheels.” This device is installed on your car's dashboard by a licensed professional (the cost of purchase and installation is usually around $500), and drivers convicted of a DUI offense in Virginia have to use it for a period of six months to one or two years.

Once an ignition-interlock device is installed, the only way to start your car is by blowing into a tube, which analyzes your breath for any signs of alcohol. If the device reads a blood-alcohol level of above 0.02 percent (that corresponds to one beer consumed in the previous hour), you can't start your car. In order to prevent people from getting around this system—say, by having a sober friend blow into the device in order to start the car—drivers have to submit to “rolling tests,” in which the device asks for a breath sample while driving.

Despite what many people think, a positive indication for alcohol use during a “rolling test” won't cause your car's engine to shut off, which would needlessly endanger you and other people. Rather, the car is rigged so that an alarm goes off and your lights start flashing, which will attract the attention of police and/or prompt you to pull over to the side of the road. Questions? Call the experienced DUI defense lawyers at Jarrell, Hicks & Waldman, PC for a free consultation!