Breathalyzer Defense in Illinois

The number on that machine is not the final word on your case. Breathalyzers are tools built by humans, operated by humans, and subject to human error. We know how to expose those errors.

Challenge the Evidence

Breathalyzer Results Are Not Infallible

When you see a BAC reading of 0.08% or higher on a police report, it feels like the case is already decided. The prosecution wants you to believe that number is scientific fact — irrefutable, precise, and damning. But the reality is far more nuanced.

Breathalyzer machines — including the models used by Lake County law enforcement — are sophisticated instruments that estimate blood alcohol concentration by measuring alcohol in your breath. That word "estimate" is crucial. These machines do not directly measure the alcohol in your blood. They measure alcohol vapor in your expired breath and then use a mathematical conversion factor to estimate what your blood alcohol level might be. Every step in that process introduces potential for error.

As former prosecutors, our attorneys relied on breathalyzer evidence to convict people. We know how prosecutors present this evidence to make it seem bulletproof. But we also know where the cracks are — because we saw cases fall apart when defense attorneys knew how to find them. Now that knowledge works for you.

Common Errors

How Breathalyzer Tests Go Wrong

Calibration Failures

Breathalyzer machines must be calibrated at regular intervals using known alcohol reference solutions. If a machine is overdue for calibration, was calibrated improperly, or the calibration records show inconsistencies, every result it produces is suspect. We subpoena maintenance and calibration logs going back months before your test.

Operator Certification Lapses

In Illinois, only certified operators may administer evidentiary breath tests. Certification requires specific training and must be kept current. If the officer who administered your test had an expired certification, incomplete training, or didn't follow proper testing procedures, the results may be inadmissible.

20-Minute Observation Violation

Illinois requires a continuous 20-minute observation period before a breath test. The officer must ensure you don't eat, drink, smoke, vomit, or belch — any of which can introduce mouth alcohol that falsely inflates readings. If the officer was distracted, left the room, or didn't start the timer properly, this requirement was violated.

Residual Mouth Alcohol

Alcohol trapped in dental work, dentures, or gum tissue can produce dramatically inflated breath readings. A tiny amount of residual alcohol in the mouth can overwhelm the breath sample, making the machine read mouth alcohol vapor instead of deep lung air. This is precisely what the 20-minute observation period is supposed to prevent — and why violations of it are so significant.

Medical Conditions

GERD / Acid Reflux: Causes stomach contents (including alcohol) to rise into the esophagus and mouth, contaminating breath samples. Diabetes: Can produce acetone (isopropyl alcohol) that some breathalyzers misidentify as ethyl alcohol. Hypoglycemia and ketogenic diets can produce similar ketone interference.

Rising Blood Alcohol

Alcohol takes 30-90 minutes to fully absorb into the bloodstream. If you had your last drink shortly before driving, your BAC may have been below 0.08% while you were actually driving but continued to rise after the stop. By the time the breath test was administered, your BAC may have crossed the legal limit — even though you were under the limit when behind the wheel.

Two Different Tests

Roadside PBT vs. Station Breathalyzer

There are two breath tests in an Illinois DUI case, and they have very different legal significance.

Preliminary Breath Test (PBT)

The roadside portable breath test is a screening tool used at the scene. Under Illinois law, PBT results are generally not admissible as evidence of your BAC at trial. They can only be used to establish probable cause for your arrest. The PBT is a less precise device, and its results are considered unreliable for evidentiary purposes. You have the right to refuse a PBT without triggering the statutory summary suspension.

Evidentiary Breath Test (Station)

The breath test at the police station — typically an Intoxilyzer 8000 or similar certified device — is the evidentiary test that the prosecution will attempt to use against you in court. This test is subject to the 20-minute observation requirement, calibration standards, and operator certification rules. Refusing this test triggers the 12-month statutory summary suspension. This is the test we focus our defense challenges on.

Our Approach

How We Attack Breathalyzer Evidence

When we take on a DUI case involving breathalyzer evidence, we conduct a thorough investigation of every aspect of the testing process. Here's what we do:

1. Subpoena Machine Records

We request the complete maintenance and calibration history of the specific device used in your test. This includes calibration dates, reference solution lot numbers, repair records, error logs, and any out-of-tolerance readings. Gaps in calibration schedules or documented malfunctions undermine the reliability of your specific result.

2. Verify Operator Credentials

We confirm that the officer who administered your test had current, valid certification at the time of testing. We also examine whether the officer followed all required procedures — including the observation period, proper test sequencing, and documentation requirements.

3. Analyze the Testing Conditions

Environmental factors affect breath test accuracy. Temperature, radio frequency interference from nearby electronics, and even the subject's breathing pattern can influence results. We investigate whether anything in the testing environment could have contributed to an inaccurate reading.

4. Review Your Medical History

If you have GERD, diabetes, dental work, or other conditions that could produce false readings, we document these conditions and, when necessary, retain medical experts to testify about how they affect breath alcohol testing.

5. Calculate Rising Blood Alcohol

If there was a significant delay between your last drink and the breath test, we work with forensic toxicologists to calculate your probable BAC at the time of driving — which may have been below the legal limit, even if the station test showed otherwise.

Don't assume a high BAC reading means a guaranteed conviction. We've seen breathalyzer evidence challenged successfully at every BAC level. Call 847-520-4810 for a free case evaluation.

FAQ

Breathalyzer Defense Questions Answered

Breathalyzer devices used in Illinois have an accepted margin of error of approximately +/- 0.01%. While the Illinois State Police certify these devices, they are not infallible. Factors including improper calibration, operator error, residual mouth alcohol, medical conditions like GERD, and environmental contaminants can all produce inaccurate readings. Studies have shown breathalyzers can vary by as much as 15% from actual blood alcohol levels.

Yes, and doing so is one of the most common and effective DUI defense strategies. Your attorney can challenge the device's calibration records, the operator's certification, whether the required 20-minute observation period was followed, whether you had residual mouth alcohol, and whether any medical conditions could have affected the results. If the breathalyzer evidence is suppressed or discredited, the prosecution's case is significantly weakened.

Illinois requires that the officer observe the subject for a continuous 20-minute period before administering a breath test. During this time, the subject must not eat, drink, smoke, vomit, or put anything in their mouth. This observation period is designed to prevent mouth alcohol from contaminating the sample. If the officer fails to observe this requirement — for example, by leaving the room or being distracted — the test results may be challenged.

Yes. Gastroesophageal reflux disease (GERD), acid reflux, hiatal hernias, and similar conditions can cause stomach alcohol to rise into the mouth, producing falsely elevated readings. Diabetes and certain diets (like ketogenic diets) can produce acetone in the breath, which some breathalyzer models incorrectly read as ethyl alcohol. Even dental work with trapped alcohol can cause false results.

The roadside Preliminary Breath Test (PBT) is a portable screening device used at the scene. In Illinois, PBT results are generally not admissible as evidence of your BAC in court — they can only be used to establish probable cause for arrest. The evidentiary breath test at the police station, typically an Intoxilyzer or similar certified device, is the test whose results the prosecution will try to use against you at trial.

That BAC Number Is Not the End of Your Case

Former prosecutors who know exactly how breathalyzer evidence is presented — and how to tear it apart. Free consultation. Payment plans available. ¡Se habla español!

Call 847-520-4810 Now

Related Practice Areas

Breathalyzer defense is often combined with other strategies: challenging field sobriety tests, understanding the consequences of refusing testing, and knowing the full DUI court process. See also: first-time DUI defense and Illinois DUI penalties.

Our attorneys have successfully challenged breathalyzer evidence to win acquittals — see our not guilty verdict from a breathalyzer challenge case result. For a comprehensive look at our DUI defense practice, visit our main site. View all of our DUI case results.

Defending clients across Lake County: Waukegan, Vernon Hills, Mundelein, Highland Park, and all surrounding communities.