Many states require a person convicted of DUI to install an ignition interlock device on their car. The ignition interlock device functions much like a breathalyzer machine as it detects whether or not the driver of a vehicle has consumed alcohol. In most cases, the ignition interlock device will prevent the driver from starting the vehicle if it measures a BAC in excess of .02. Much like breathalyzer machines used in DUI cases, however, the ignition interlock device is problematic. According to a study conducted by the National Highway Traffic Safety Administration, most of these devices tests fail to produce accurate readings, particularly at “low” (.05 BAC) and “moderate” (.08 BAC) levels. See Workshop on In-Vehicle Alcohol Test Devices, NHTSA DOT HS-807-145 (Sept. 1986).
In addition, an ignition interlock device can produce false-positive results just like the conventional breathalyzer machine. The most common cause of such false-positives appears to be the existence of “mouth alcohol” — alcohol that is present in a person’s mouth and has not yet had time to dissipate completely into the blood. Aside from traditional alcoholic beverages, mouth alcohol is often present in high quanities after a person ingests mouthwash, cough syrup, breath spray, or even salad dressing, all of which contain sizeable amounts of alcohol.
There have also been numerous reports of false-positive results after a driver fills up at a gas station because the gasoline fumes register much the same way traditional alcohol does.