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Are breath test devices accurate?

On Behalf of | Mar 29, 2021 | Traffic Offenses And DUI

Law officers in Illinois and throughout the United States use roadside breath test devices to determine whether drivers have a blood alcohol content level that is over the legal limit of 0.08. If you have ever been pulled over on suspicion of drinking and driving, you may have been asked to submit to one of these tests.

Yet even if the device shows you have a BAC level of 0.08, the results may not be accurate. Studies from the State University of New York at Potsdam show that many of these tests show inflated results. In fact, researchers at the university found that at least 23% of those tested using a roadside breath test device had inflated results.

How do breath test devices work?

Rather than determine the alcohol content in an actual blood sample, breath tests measure the amount of ethanol alcohol in an exhaled breath sample. When breath test readings are compared to the results from actual blood tests, the numbers showed a 15% discrepancy. This significant difference may result in an erroneous DUI charge or conviction.

What factors affect breath test results?

In addition to measuring ethanol in your breath sample, breath test devices may detect other substances that have similar methyl structures. The factors that can influence breath test results include the following:

  • Relative humidity and temperature of the air
  • Cigarette smoke, pollution and dirt in the air
  • Fumes from cleaners, gasoline and paint
  • Residual vomit, food, drink and blood in the mouth
  • Electrical interference from cellphones and police radios

Furthermore, officers administering the tests must ensure the devices are calibrated correctly and use them properly in order to maximize result accuracy.