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Are breath test devices reliable?

In Illinois, and in most other states across the nation, it is illegal to drive with a blood alcohol content level of 0.08 or higher. In some cases, people who have a BAC level of 0.05 can be arrested as well. If you are pulled over on suspicion of drinking and driving, an officer may ask you to submit to a roadside breath test. These devices are used to determine your BAC level without actually taking a blood sample. The problem lies in the fact that these devices do not always yield accurate results, which could lead to a wrongful DUI arrest. 

Breath test devices work by measuring the amount of ethanol alcohol in an exhaled breath sample. It then takes this number and converts it to a blood alcohol level. Yet, the device is known to pick up other substances that have a similar chemical structure to ethanol. Furthermore, other factors can influence the readings. According to the State University of New York at Potsdam, these factors include the following:

  • Pollution and smoke in the air

  • Relative humidity and temperature

  • Residual blood, vomit, food and liquid in a person’s mouth

  • Cigarette smoke and fumes from cleaners and gasoline

  • Electrical interference from cell phones and/or police radios

Breath test devices must also be calibrated properly in order to produce reliable results and work correctly within a certain humidity and temperature level. If the officer using the device does not do so properly, the machine can produce erroneous results as well. 

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