How does alcohol breath testing work?

Posted on behalf of Donahue & Walsh, P.C. | September 29, 2022

A breathalyzer test is one of the most common tests for a potential DUI. But do you know how they work to collect an accurate blood alcohol concentration (BAC)? Continue reading to find out.

How They Are Used

Preliminary breathalyzer tests (PBT) are the breath tests requested on the side of the road, which are about the same size as old cell phones. A breath test is also requested once at the police station, where a driver blows into a larger machine. If a driver agrees to submit to a breath test, they first blow into a disposable mouthpiece. Their breath is then sent through the device, which offers results measuring the content of alcohol in the driver’s breath.

The Technology

Breath testing devices use either a fuel cell or an infrared cell to measure BAC. The infrared cell directs infrared energy through the sample; any unabsorbed energy is detected on the other side. The higher the ethanol concentration, the more infrared absorption occurs. This interaction is much like how sunglass lenses absorb sunlight; alcohol absorbs infrared light. The ethanol concentration is then analyzed by the device to give a reading.

Are They Always Accurate?

Unfortunately, breathalyzer tests are not always accurate. Their accuracy can depend on factors such as the breath sample, gender, or medication. For example, if the driver does not take a full breath before blowing, their results may not be accurate regarding their BAC.

If you or a loved one is facing a DUI conviction, contact our team at 815-344-8860. You should not try to fight it alone. We can help you fight for your freedom and future. Remember, anything you say to the police can and will be used against you. Contact us before it is too late to discuss your legal defense options.

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