If you have ever been pulled over on suspicion of drinking and driving in Wisconsin, you may have been asked to take a breath test. Law enforcement officers often use these devices to measure drivers’ blood alcohol content level and determine whether they are over the legal limit of 0.08. Yet, studies show that the results of roadside breath test devices are not always accurate, and in some cases, wrongful readings could lead to a wrongful DUI charge. In fact, the results can vary by at least 15% in some cases. At least one in four people who take the test may show inflated results.

When an officer asks you to exhale into a hand-held breath test device, the machine measures the amount of ethanol alcohol in your breath sample. It then converts this number into a blood alcohol level, without actually measuring the amount contained in your blood. A study by the State University of New York at Potsdam found that the machines also measure substances that have a similar molecular structure to ethanol, and that there are many factors that can alter your exhaled breath sample. This can throw off the accuracy of your reading. Some of these factors include the following:

  • Residual food, drink, blood or vomit in the mouth
  • Gasoline, cleaning fluid and exhaust fumes
  • The temperature and humidity of the air
  • Cigarette smoke and other pollution in the air
  • Interference from cell phones or police radios

Breath test devices may also give erroneous readings when they are not calibrated properly or the administering officer does not use the machine correctly.

This information is intended to educate and should not be taken as legal advice.