Frequently Asked Questions - Breath Tests

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How does the Breath Test Actually Work?

Most people have heard of a “breathalyzer” but few people know how it actually works. The machine Minnesota uses is called the DataMaster Transportable with Fuel Cell Option (“DMT” for short). The DMT measures alcohol by a process called infrared spectroscopy. Essentially, the subject blows into the breath tube and the breath travels through the tube to a sample chamber. In the sample chamber, the machine flashes an infrared light from one side to the other. On the other side of the chamber is a sensor. The sensor measures how much infrared light was absorbed on its way through the chamber to determine breath alcohol concentration.

While this technology has its benefits, there are problems as well. One problem is interfering substances. Some substances that are not alcohol resemble alcohol on a molecular level. Sometimes, these similar molecular structures absorb infrared light in the same way alcohol does, and the machine erroneously believes the substance is alcohol. The two most common interferants are acetone and isopropanol. People who vigorously exercise routinely have higher acetone levels, as do people engaged in low carb diets or the keto diet.

Another problem with infrared spectroscopy in mouth alcohol. If a subject has alcohol in their mouth that has not been digested, that can supply alcohol to the chamber that is not reflective of the person’s true breath alcohol content. An officer administering the DMT is supposed to observe a subject for at least 15 minutes prior to the test to ensure nothing enters the subject’s mouth from the inside (e.g. burping, belching, or vomiting) or the outside. If the officer fails to do this the test is not scientifically reliable.

The science and procedures associated with the DMT are complex. If you are charged with an alcohol-related driving offense, you should contact an experienced DWI attorney. Our attorneys are available to consult with you or your loved ones. Speak with a defense lawyer at (612) 334-3342 today.

Posted 03-04-2026

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