What Happens if I Have a “False Positive” Test Result on my Ignition Interlock Device?

Many people who are convicted of a DUI are now being required to install an ignition interlock device (IID) in their vehicle. This device requires a breath sample that measures the driver’s blood alcohol content (BAC) before the driver can start the vehicle. If the driver registers a blood alcohol content of over a certain amount, the vehicle cannot be started. Still, many drivers fear a a “false positive” reading, and may be confused about what can cause that to occur. The reality is that IIDs are almost always accurate, but, there are a few things that can cause a false positive reading.

Mouthwash is one thing that can sometimes cause a false positive result on an IID as many brands of mouthwash contain alcohol. If a driver recently used mouthwash, even if they did not ingest any, they can still register a blood alcohol content of up to .25. To avoid this, people who frequently use mouthwash should rinse their mouth with water after using mouthwash and wait at least ten minutes before using the ignition interlock device. This should help to avoid false positive readings on the IID.

A surprising thing that can sometimes cause a false positive is spicy food. Spicy food reacts with the chemicals found in everyone’s stomach and results in the production of methane gas. In some instances this methane gas can cause a false positive reading. Fortunately, taking an antacid can remedy this.

An ignition interlock device can also, on rare occasion, malfunction and cause a false positive result. If this happens, the driver should contact their IID service provider immediately, as the result will still be recorded, and the service provider can provide instructions and assistance to help maintain a sober IID record.

If a device registers a false positive, chances are that by waiting a few minutes and trying again it will work. By knowing the triggers for false positive readings on an IID it is possible to avoid the inconvenience of having to submit a retest. These reasons for a false positive are not an excuse for having high blood alcohol content because of alcohol consumption. But, they can help explain how a false reading may happen.