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How breathalyzers may provide false positives

On Behalf of | Jan 19, 2018 | Blog

If police officers stop you and suspect a DUI, they will likely ask you to take a breathalyzer test. People who get a result of blood alcohol content exceeding the legal limit of 0.08 percent often assume there is no point in fighting the charges that ensue. How can you argue with machine-generated, scientifically-backed results?

The truth is that breathalyzers can deliver inaccurate results for a number of reasons. Experienced defense attorneys know to examine all aspects of a case and build a solid strategy. Speaking with a lawyer, rather than just assuming the worst, may reveal you have a stronger defense than you thought.

Operator error

A machine is only as effective as the operator. Not all police officers know how to properly use the breathalyzer or ensure it is well-maintained. Common operator errors include failing to make sure the mouthpiece is completely clean (or changed) after each use, creating the possibility that residual alcohol on the piece affects later results. Manufacturers also stress the importance of regular calibration.

Defective machines

Like any other products on the market, breathalyzers can suffer from defects that affect results. In a Massachusetts case, it is argued that evidence came to light that errors previously attributed to operator error actually resulted from faulty machines and that more tests may have been affected than previously believed.

Health conditions

In other cases, false positives can occur due to medical conditions that generate ketone production, such as poorly controlled diabetes, as this test can read ketones as alcohol.

Mouth alcohol

Because the breathalyzer measures the percentage of alcohol in the air you exhale from your lungs, the presence of alcohol in your mouth or on your clothing can yield a falsely high percentage. People may tend to retain alcohol from a small drink or even alcohol-based mouthwash if they have dentures or other surfaces where alcohol could pool.


Those who work in environments with high amounts of acetone, such as painters or nail salon workers, may also fail a breathalyzer test, as their skin, hair and clothing could retain enough acetone for this to happen.