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Chicago Breathalyzer Test

The breathalyzer is the central piece of chemical evidence in most Illinois DUI cases. Officers commonly use two distinct types of breath tests during a Chicago DUI investigation: a roadside Portable Breath Test (PBT) and a station-based evidentiary breath test. The two have very different legal weight, different procedural requirements, and different challenge opportunities.

The Roadside Portable Breath Test

The PBT is a small handheld device the officer may offer to use during the traffic stop, before any arrest decision. The PBT serves a narrow legal purpose: it gives the officer one more piece of information for the probable cause determination. It is not admissible at trial to prove BAC. It is admissible only for the limited purpose of probable cause review at a suppression hearing.

The PBT is voluntary in Illinois. A driver can refuse the PBT without triggering the implied consent suspension that applies to the station test. Refusing the PBT does not increase or decrease the criminal exposure, but it does remove one piece of evidence from the probable cause calculation. Whether refusing makes sense depends on the specific situation; in most cases, declining the roadside PBT is the more conservative choice.

The Station Evidentiary Breath Test

The evidentiary breath test is the one that matters for the criminal case and the Statutory Summary Suspension. It is administered at the police station on an approved instrument by a certified operator following the procedure required by 20 Illinois Administrative Code Section 1286.

The Test Procedure

  1. The subject is transported to the testing location and held there.
  2. The operator conducts a 20-minute observation period during which the subject cannot eat, drink, smoke, vomit, regurgitate, or have anything in their mouth.
  3. The operator runs the instrument through its startup procedure, including ambient air checks.
  4. The subject blows two samples into the mouthpiece, producing a deep lung air sample of sufficient volume.
  5. The instrument prints a result showing both samples, the time of each, and the calculated BAC.

Refusing the Station Breath Test

Illinois implied consent law treats refusal of the station breath test as a separate matter from the underlying DUI charge. Refusal triggers an automatic Statutory Summary Suspension:

  • First refusal: 1 year suspension.
  • Second refusal within 5 years: 3 year suspension.

The refusal suspension takes effect on day 46 after the arrest unless the driver requests a hearing within 90 days. See our Secretary of State information page for hearing procedures.

Refusal also tells the prosecution they need a warrant to obtain blood evidence. In serious cases involving accidents or injuries, prosecutors and officers typically pursue a warrant. The refusal does not block the prosecution from getting chemical evidence; it just changes the path.

Common Breathalyzer Challenges

The 20-Minute Observation Period

The observation period requirement is one of the most violated and most successfully challenged elements. Bodycam review often shows the officer was distracted, the subject moved an object in their mouth, or the period actually started later than the log indicates. A successful observation period challenge often results in suppression of the breath result.

Calibration and Maintenance Records

Illinois requires instruments to be calibrated and certified on a defined schedule using simulator solutions of known concentration. Calibration records are subject to discovery. A Chicago DUI lawyer routinely subpoenas:

  • The instrument's calibration logs for the period before and after the test.
  • Records of any maintenance, repair, or adjustment to the instrument.
  • Simulator solution certifications and expiration dates.
  • The certification records of the personnel performing the calibration.

Operator Certification

The Breath Analysis Operator must be certified at the time of the test. Certification documents and any lapses are subject to discovery and challenge.

Instrument Error Codes

Breathalyzers log internal events including error codes, aborted tests, and out-of-range results. Errors in the logs near the time of the suspect's test can call the result into question.

Mouth Alcohol Sources

Belching, regurgitation, recent ingestion, certain medications, oral piercings, and conditions like GERD can all produce mouth alcohol artifacts that elevate the apparent BAC. See our breath evidence page for the full list.

Breath Temperature

The standard breath temperature assumption used by the instrument may not match the subject's actual breath temperature. Variation can shift the reading by 6 to 8 percent per degree Celsius.

Should I Take the Breathalyzer Test?

The decision to take or refuse the breath test is a personal one with significant consequences either way. Some considerations:

  • If you take the test and pass below .08, the BAC component of the DUI prosecution is removed. The case may still proceed on observation evidence, but the strongest prosecution evidence is gone.
  • If you take the test and fail, the BAC becomes part of the case, but the suspension is shorter (6 months if under 5,000 prior driving privileges).
  • If you refuse, no BAC is in evidence directly, but the suspension is longer (1 year first refusal, 3 years subsequent).
  • If you refuse, the prosecution may pursue a warrant for blood. Whether they do depends on the seriousness of the case.

This is not legal advice for any specific situation. A Chicago DUI lawyer who knows the specific facts of your stop and arrest can advise on the implications of either choice.

Related Pages

Additional Chicago Legal Resources

Frequently Asked Questions

Can someone request a retest after an Illinois breathalyzer reading?

Yes. Illinois allows a person tested by law enforcement to obtain an additional independent chemical test at the subject's own expense under 625 ILCS 5/11-501.2. The law requires the arresting agency to allow reasonable opportunity but does not require the agency to transport or arrange the independent test. The subject typically arranges a blood test at a hospital shortly after release. The independent result becomes admissible and can contradict the state's number, particularly on borderline cases where absorption or elimination timing matters. Denial of a reasonable opportunity may support suppression of the state's test. A Chicago DUI lawyer confirms opportunity was given and, when denied, files the motion.

Do medical conditions affect Illinois breathalyzer test results?

Yes. Medical conditions can materially affect Illinois breathalyzer results. GERD and hiatal hernia allow stomach alcohol to reflux into the mouth during the exhalation, producing mouth alcohol contamination that overstates BAC. Diabetic ketoacidosis produces acetone the machine may misread. Recent dental work, oral piercings, and dentures can trap alcohol. Asthma and COPD affect the ability to deliver an adequate sample, and repeated failed attempts can be scored as refusal. Certain medications and diets producing ketones create similar interference. Under Illinois evidentiary standards the state does not have to affirmatively rule these out, but a documented medical history creates reasonable doubt. A Chicago DUI lawyer builds the medical record into the defense.

What are the consequences of refusing a breathalyzer in Illinois?

Refusing an evidentiary breath test in Illinois triggers 625 ILCS 5/11-501.1 Statutory Summary Suspension consequences. A first-offender who refuses faces a 12-month suspension; a non-first-offender faces 36 months. Refusal also blocks MDDP eligibility for repeat offenders and can be introduced at the criminal trial as consciousness of guilt. There is no criminal penalty for refusal beyond the suspension and evidentiary use. Refusal of a Portable Breath Test carries no suspension because the PBT is voluntary. Choosing whether to refuse is case-specific; there is no universal right answer. A Chicago DUI lawyer analyzes the tradeoff based on BAC likelihood, prior record, and license needs.

What factors affect the accuracy of an Illinois breathalyzer test?

Illinois breathalyzer accuracy depends on machine calibration, operator technique, subject physiology, and environmental conditions. Instrument-level factors include certification currency, accuracy check history, and RFI shielding. Operator-level factors include the 20-minute observation, proper mouthpiece use, and correct sample delivery. Subject-level factors include GERD, diabetic ketoacidosis, dentures with alcohol residue, recent oral use of mouthwash or breath spray, and hematocrit. Temperature, atmospheric conditions at the station, and elapsed time since the last drink all affect the result. Under 625 ILCS 5/11-501.2 the state must lay foundation, but individual accuracy remains contestable at trial through experts. A Chicago DUI lawyer builds these variables into cross-examination.

What is the difference between a Portable Breath Test and a station-based breathalyzer?

Illinois distinguishes the Portable Breath Test from the evidentiary breath machine. The PBT is a roadside handheld device used for pre-arrest screening. Its numerical reading is not admissible at trial on the guilt phase, though its result can support probable cause. The station-based evidentiary instrument, typically an EC/IR II or Datamaster, is calibrated, certified, and operated under Illinois State Police rules and 20 Ill. Adm. Code 1286. Its result is admissible under 625 ILCS 5/11-501.2 when foundation is proven. The 20-minute observation, operator permit, and calibration rules apply only to the evidentiary test. A Chicago DUI lawyer keeps the PBT number out of the guilt phase entirely.