Chicago Criminal Lawyer Blog
When the Machine Says You’re Guilty
On a cold Chicago night, a driver is pulled over near Wrigleyville after an officer claims he rolled through a stop sign. The streets are wet, visibility is low, and he’s just leaving a friend’s birthday dinner. A few minutes later, after field sobriety tests on an uneven sidewalk, he’s at the station blowing into a breathalyzer. The result flashes: 0.11% BAC.
In the eyes of the arresting officer, and maybe even the prosecutor who will later review the case, the number tells the whole story. But Illinois law doesn’t convict people based solely on what a machine says. That number is only evidence, and like all evidence, it can be challenged.
In Illinois, DUI is prosecuted under 625 ILCS 5/11-501, and a reading of 0.08% or higher is enough for a charge. A first DUI is a Class A misdemeanor, carrying up to a year in jail, thousands in fines, and a license suspension. Certain factors — prior DUIs, transporting minors, crashes causing injury — turn it into an aggravated DUI, which is a felony carrying potential prison time.
For a defendant, the stakes are enormous. Jail time is only part of it. A conviction can cost a career, raise insurance rates, and leave a permanent record that can’t be sealed or expunged in Illinois.
The Road From Stop to Courtroom
Most breathalyzer-based DUI cases follow a predictable path in Chicago. An officer makes a traffic stop. Signs of possible impairment — odor of alcohol, red eyes, slowed speech — lead to field sobriety tests. If the officer claims the tests were failed, a formal arrest is made.
Illinois’ implied consent law means drivers are automatically considered to have agreed to chemical testing if arrested for DUI. Refusing the breath test will trigger a statutory summary suspension of driving privileges — 12 months for a first refusal, 36 months for a repeat within five years. Taking the test and blowing 0.08% or above will trigger its own suspension, even if the case hasn’t been to court yet.
The criminal side begins with charges filed by the State’s Attorney. In Cook County, misdemeanor DUI cases may be heard in local branch courts, while felony DUI cases go to the main criminal courthouse at 26th and California. From there, the defense strategy begins to take shape.
Why Breathalyzer Evidence Is Not Ironclad
A breathalyzer doesn’t draw blood. It uses a chemical reaction or infrared spectroscopy to measure alcohol in the breath, then uses a mathematical formula to estimate blood alcohol concentration. That estimate can be wrong.
Calibration is critical. Illinois State Police regulations require that evidentiary breath testing instruments be inspected and certified regularly. If the logs are missing or show skipped maintenance, the accuracy is suspect.
Human error plays a role as well. Operators must be certified and must observe the subject for at least 20 minutes before the test to ensure no burping, vomiting, or consumption of any substance occurs. Skipping this step can contaminate the sample.
Even certain medical conditions — like GERD, which can cause alcohol vapors from the stomach to enter the mouth — can falsely elevate BAC results. Diabetic ketoacidosis can have a similar effect. Environmental factors like gasoline fumes in a garage or industrial cleaning chemicals can also interfere.
A Case Where the Number Fell Apart
A Chicago defense case involved a woman arrested after leaving a corporate holiday party downtown. Her breathalyzer reading was 0.09%, just above the limit. The defense obtained the breathalyzer’s maintenance records and discovered it had been taken out of service for repairs the month before but returned to use without a complete calibration check.
The defense filed a motion to suppress the breath test results. During the hearing, cross-examination revealed that the officer who performed the test wasn’t aware of the calibration gap. The judge ruled the test inadmissible. Without BAC evidence, and with video showing her walking steadily and speaking clearly, the prosecution dismissed the DUI charge.
How the Criminal Defense Process Unfolds
After arrest, the defendant attends a first appearance, where conditions of release are set. Pretrial discovery begins, allowing the defense to review all reports, video, and breathalyzer records. In breathalyzer cases, this is where the fight often starts.
Motions to suppress may be filed to challenge the legality of the stop or the reliability of the breath test. If the judge grants such a motion, the case may collapse before trial. If not, the case may move toward trial, where the defense can cross-examine the state’s witnesses, question the breathalyzer’s accuracy, and present alternative explanations for the reading.
Evidence the State Relies On
Beyond the BAC number, prosecutors in Illinois build DUI cases with:
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Officer testimony describing alleged signs of impairment.
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Field sobriety test results.
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Video evidence from squad cars or body cameras.
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Statements made by the driver.
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Witness accounts, especially in crash cases.
Each of these can be attacked. Video can contradict the officer’s account. Field sobriety tests can be compromised by poor lighting, uneven pavement, or the driver’s medical conditions. Statements may be excluded if taken in violation of Miranda rights.
Why a Defense Attorney Changes the Outcome
In Chicago and surrounding counties, DUI prosecution is aggressive. Without a defense attorney, defendants are at the mercy of the state’s narrative. An attorney knows how to spot procedural errors, subpoena calibration records, hire forensic experts, and negotiate with prosecutors for reduced charges or dismissal.
An attorney also handles the administrative license suspension hearing before the Illinois Secretary of State, which is separate from the criminal trial. Winning that hearing can mean keeping driving privileges while the case is pending.
Common Defenses in Breathalyzer Cases
Defense strategies can vary, but common ones include:
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No probable cause for the initial stop.
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Improper administration of the breath test.
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Faulty or uncertified breathalyzer equipment.
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Medical or environmental factors causing false positives.
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Lack of credible evidence of actual impairment.
These defenses are not theoretical — they’ve been used successfully in Illinois courts to secure dismissals and acquittals.
Choosing the Right Attorney for a Breathalyzer DUI
The qualities to look for go beyond years in practice. A strong Illinois DUI defense attorney understands the technical aspects of breath testing, knows the tendencies of local judges and prosecutors, and has a track record of cross-examining police officers effectively. They keep clients informed and prepared at every stage.
The Law Offices of David L. Freidberg: Fighting for Drivers Across Chicago
David L. Freidberg has built a reputation in Chicago and surrounding counties for dismantling shaky DUI cases — especially those built on questionable breathalyzer results. His firm handles cases in Cook, DuPage, Will, and Lake Counties, offering 24/7 availability for clients facing DUI charges.
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.
