All 50 states have laws on the books encouraging, and sometimes requiring, the use of ignition interlock devices by those convicted of drunk driving. These devices work by analyzing a breath sample and preventing one from starting the car if one’s blood alcohol reading is above a predetermined threshold. Their purpose is to prevent repeat drunk driving offenses while still allowing an individual to keep his or her license and continue driving to meet obligations.
According to the National Conference of State Legislatures, ignition interlock devices have been around for approximately three decades. During that time, they have gone through improvements that make false positives less common than they once were. Nevertheless, the devices are not infallible. Here are some factors that could cause a false positive.
1. Cigarette smoke
Smoking in a vehicle may be illegal when there are children present as passengers. Otherwise, there are very few legal restrictions on it. Nevertheless, people with an ignition interlock device may want to avoid smoking in the car because there are verifiable instances of cigarette smoke producing a false positive on an IID. Though a less common occurrence than it used to be with the older, less efficient devices, it is still a risk.
2. Personal hygiene products
Quite a few personal hygiene products have alcohol as an ingredient. These include mouthwash and hand sanitizer. An ignition interlock device may detect alcohol on one’s breath after one has used mouthwash, even if one spit it out as instructed rather than swallowing it.
Alcohol-based hand sanitizer is effective at killing germs. Before it dries completely, however, it produces fumes that an IID may detect. A driver should allow at least 15 minutes after using any of these products before driving.
According to Men’s Health, ketosis occurs when the body lacks adequate fuel so the liver breaks down fat cells. People on the ketogenic diet avoid eating carbohydrates to induce this state with the goal of losing weight. Ketosis may produce a false positive on a breath device because the process of breaking down fat cells produces a byproduct of isopropyl alcohol. The device may mistake this with ethanol found in alcoholic beverages.
A false positive on an IID can result in additional penalties. It may increase the amount of time a driver needs to keep the device in place, as well as incur fines.