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Can I Challenge the Accuracy of a Breathalyzer in My Illinois DUI Case?
Chicago, Illinois and the Law on Breathalyzer Evidence
Chicago is a city with constant traffic and an equally constant law enforcement presence. DUI arrests happen every day across the city, from the Kennedy Expressway to the streets of Englewood, Lakeview, and Humboldt Park. Illinois DUI law, under 625 ILCS 5/11-501, makes it illegal to operate a motor vehicle while under the influence of alcohol, drugs, or intoxicating compounds. For alcohol cases, the most common tool police use is the breathalyzer.
The law presumes intoxication if a driver’s blood alcohol concentration (BAC) is 0.08% or higher. For commercial drivers, the limit is 0.04%, and for drivers under 21, Illinois has a zero-tolerance policy. These numbers come almost exclusively from breathalyzer machines. Because these readings carry so much weight in court, defendants often assume they cannot be questioned. That is a mistake. Breathalyzer devices are not infallible, and Illinois courts recognize that their results can be challenged.
Illinois prosecutes DUI charges as either misdemeanors or felonies. A first or second DUI without aggravating factors is generally a Class A misdemeanor, punishable by up to 364 days in jail and fines up to $2,500. If the DUI involves an accident causing great bodily harm, death, or multiple prior convictions, it becomes an Aggravated DUI, a felony with the potential for years of prison time. This makes challenging the accuracy of breath test results critical to protecting your future.
How Illinois DUI Cases Begin and the Investigation Process
A DUI case usually starts with a traffic stop. Officers may pull a driver over for swerving, speeding, or a minor traffic violation like rolling through a stop sign. Once contact is made, the officer looks for signs of alcohol consumption — bloodshot eyes, the odor of alcohol, or slurred speech. In Chicago, these observations are often recorded by dashcams and body-worn cameras, which can later become key evidence.
If impairment is suspected, the officer may ask the driver to perform field sobriety tests. These tests — the walk-and-turn, one-leg stand, and horizontal gaze nystagmus — are designed to detect coordination issues, but they are highly subjective. Conditions such as nervousness, fatigue, or even bad weather can influence performance.
The officer may then request a preliminary breath test (PBT) at the roadside. This handheld device gives an estimate of BAC but is not admissible in court to prove intoxication; it is used only to establish probable cause for arrest. If arrested, the driver is transported to the police station, where they are asked to submit to an evidentiary breath test using a machine like the Intoximeter EC/IR II.
At this point, Illinois’ implied consent law applies. Under 625 ILCS 5/11-501.1, by driving in Illinois, every driver is deemed to have consented to chemical testing if arrested for DUI. Refusal to submit to a breath test results in an automatic statutory summary suspension of driving privileges — 12 months for a first refusal, 36 months for subsequent refusals. Taking the test and failing (BAC of 0.08 or higher) triggers a shorter suspension, but the result is used as evidence in court.
The Arrest Process, Evidence Collection, and How Breathalyzers Work
Once a driver is placed under arrest, they are transported to a district station or central testing facility. The breathalyzer test is administered after a required observation period — usually 20 minutes — during which the officer must ensure that the driver does not burp, vomit, or place anything in their mouth that could affect the reading. The machine then requires two breath samples, and the results are recorded.
Law enforcement collects additional evidence during this process, including:
- Officer reports detailing observations of driving behavior
- Field sobriety test results
- Video recordings from squad cars or body cameras
- Witness statements if an accident occurred
- Statements made by the driver during questioning
Breathalyzers measure alcohol by detecting the concentration of ethanol molecules in deep lung air. The device then uses a ratio to estimate blood alcohol concentration. But this process is vulnerable to errors. Factors such as calibration, temperature, medical conditions, and even diet can influence results. For example, a driver with acid reflux or diabetes may produce a falsely high BAC reading.
Penalties, Punishments, and Collateral Consequences
If convicted of DUI in Illinois, penalties vary depending on whether the case is a misdemeanor or felony. For a first conviction, penalties may include:
- Up to one year in jail
- Fines up to $2,500
- Mandatory alcohol education or treatment
- Driver’s license suspension or revocation
A second DUI conviction can carry mandatory minimum jail time or community service, while a third conviction is an Aggravated DUI, a Class 2 felony with a potential prison sentence of 3 to 7 years. If the offense resulted in death, it becomes a Class 2 felony punishable by up to 14 years in prison.
Collateral consequences extend beyond court-imposed penalties. A DUI conviction in Illinois is not eligible for expungement or sealing. This means it remains on your record permanently, visible to employers, landlords, and licensing agencies. Insurance rates skyrocket, and professional licenses in fields such as nursing, teaching, and commercial driving may be suspended or revoked.
The Trial Defense Process and a Chicago Example
DUI trials in Illinois begin with arraignment and pretrial motions. Defense attorneys often file motions to suppress the breathalyzer results, arguing that the machine was improperly calibrated, the test was improperly administered, or the officer lacked probable cause to arrest. If the court agrees, the breathalyzer evidence may be excluded, significantly weakening the State’s case.
At trial, the prosecution must prove beyond a reasonable doubt that the defendant was operating a motor vehicle while under the influence. The defense may challenge the breathalyzer results with expert testimony, question the officer’s training, and highlight inconsistencies in the evidence.
Imagine a case in Logan Square where a driver is pulled over for speeding slightly over the limit. The officer claims the driver smelled of alcohol and performed poorly on field sobriety tests. At the station, the breathalyzer shows a BAC of 0.09. The defense attorney investigates and finds that the machine was overdue for state-mandated certification under Illinois Administrative Code standards. The defense files a motion to exclude the results, and the judge agrees. Without the breath test, the prosecution’s case relies only on subjective observations, leading to an acquittal.
Defenses Against Breathalyzer Evidence
Common defenses include:
- Machine not properly calibrated or maintained
- Officer failed to follow observation period requirements
- Medical conditions or diets (acid reflux, diabetes, ketogenic diet) caused false positives
- Mouth alcohol contamination from recent use of mouthwash or dental work
- Lack of proper certification for the operator or the machine
- Chain of custody errors with testing records
Because the State often relies heavily on the breathalyzer to secure convictions, undermining its accuracy can be the difference between conviction and dismissal.
Why You Need an Attorney at Every Stage
From the moment of the traffic stop, legal representation is critical. An attorney can challenge the legality of the stop, scrutinize the officer’s conduct, demand maintenance records for the breathalyzer, and retain expert witnesses to testify about the unreliability of the results. During plea negotiations, a defense attorney can use these weaknesses to push for reduced charges or alternative sentencing. At trial, the attorney presents the defense strategy, cross-examines officers, and argues reasonable doubt.
Without representation, defendants risk being railroaded by the State’s reliance on a machine that is not always accurate.
Qualities to Look For and Questions to Ask
When hiring a Chicago DUI defense lawyer, look for extensive trial experience, a strong record of challenging chemical testing, and familiarity with Cook County judges and prosecutors.
Questions to ask during a consultation include:
- How often do you challenge breathalyzer results?
- What strategies have you used successfully in similar cases?
- Do you work with toxicology experts?
- How do you approach pretrial motions to suppress?
- What are the likely outcomes in my case?
Chicago DUI FAQs
Can I refuse a breathalyzer test in Chicago?
Yes, but refusal results in an automatic driver’s license suspension under Illinois’ implied consent law. The refusal may also be used against you in court.
If I blow over the limit, is my case hopeless?
No. Breathalyzer results can be challenged on numerous grounds, including calibration, operator error, and medical conditions. Many DUI cases with “failed” tests end in dismissals or acquittals.
How often are breathalyzers calibrated in Illinois?
Machines must be certified every 62 days under Illinois Administrative Code. If records show lapses, results may be inadmissible.
What happens if my license is suspended after a DUI arrest?
You may be eligible for a Monitoring Device Driving Permit (MDDP) with a Breath Alcohol Ignition Interlock Device (BAIID). Your attorney can help you apply.
Will a DUI show up on background checks in Illinois?
Yes. DUI convictions are permanent and cannot be sealed or expunged. They appear on criminal and driving records indefinitely.
Are field sobriety tests reliable in drug or alcohol cases?
They are highly subjective and influenced by fatigue, nerves, weather, and medical conditions. They are often challenged in court.
Can I represent myself in a DUI case?
Technically, yes, but it is a major mistake. DUI law is complex, and prosecutors rely on scientific evidence that requires expert cross-examination. Without an attorney, you are at a serious disadvantage.
Why Defendants Need an Attorney and Why Choose David L. Freidberg
Challenging breathalyzer evidence requires legal skill, scientific knowledge, and courtroom experience. Defendants who try to handle these cases alone face prosecutors who are trained to present breathalyzer results as airtight proof. Without an attorney, you risk conviction, loss of license, and long-term consequences on your record.
The Law Offices of David L. Freidberg has decades of experience challenging DUI charges across Chicago and surrounding counties. Our firm understands how breathalyzer machines work, how they fail, and how to expose those weaknesses in court.
When You Need a Fighter, Call Us!
If you were arrested in Chicago, protect your future by contacting The Law Offices of David L. Freidberg. We have decades of experience handling DUI cases in Illinois. Our firm is available 24/7 to provide the legal defense you deserve.
Contact us today at (312) 560-7100 or toll-free at (800) 803-1442 for a free consultation. We’re available 24/7 to serve clients throughout Illinois, Cook County, DuPage County, Will County, and Lake County.