Chemical breath testing is so common that it is part of mainstream culture. High schools sometimes buy chemical testing units to check students during class or special events for impairment. People who drink frequently may have their own pocket device, or the bar that they visit may have a public unit that you can pay to use before leaving the establishment.

Police officers stop and test drivers who show signs of impairment. Many people place a lot of faith in chemical breath testing without understanding how it actually works. The science of how chemical breath tests work shows how these tests can make mistakes.

The testing unit is intended to establish the volume of alcohol in your blood

There is a correlation between the level of alcohol in your bloodstream and the amount that you will exhale during a chemical breath test. Using information about that correlation, chemical test units convert exhaled air samples in to digital readouts that indicate a specific blood alcohol concentration (BAC).

When someone breathes in to the testing unit, the device checks the sample for the presence of alcohol molecules. It may create a false positive for similar molecules that are not alcohol. It will then try to determine the likely level of alcohol in your bloodstream based on the amount present in the breath sample.

At a traffic stop, if the unit returns a test result with a BAC higher than the legal limit for your age and licensing status, you might face arrest and criminal charges for drunk driving. Understanding how a breath test works can be the first step toward building a defense strategy. Your attorney can look at all of the evidence and provide guidance on the best way to proceed.