How to Challenge Breathalyzer Results in a DUI Case

A breathalyzer reading of 0.08 or higher feels like a closed case. The machine said so, and machines do not lie, right? In reality, breath test results are far more fragile than most people realize. They depend on a device that needs regular calibration, a police officer who must follow strict procedures, and a body of science that has been challenged in courtrooms for decades. Thousands of DUI defendants every year learn that the number on the ticket is not the final word. Understanding how to challenge breathalyzer results in a DUI case can mean the difference between a conviction that follows you for years and a dismissed or reduced charge. This guide explains the most common weaknesses in breath testing, the legal steps involved, and when it makes sense to bring in a defense attorney.

Why Breathalyzer Results Are Not Beyond Question

A breathalyzer does not measure alcohol in your blood directly. It estimates blood alcohol concentration (BAC) by measuring ethanol vapor in the air you exhale, then applying a mathematical conversion ratio. That ratio assumes an average person with average body temperature, average lung capacity, and average breathing patterns. Anyone who falls outside those averages can register a higher BAC than their blood would actually show. Courts and scientists have recognized this gap for years, which is why breath evidence is treated as an estimate rather than a precise measurement.

Several well documented sources of error can inflate a reading. Mouth alcohol from recent drinking, burping, vomiting, or even using certain breath sprays can concentrate alcohol in the mouth and skew the sample. A device that has not been calibrated or that uses expired simulator solution can drift out of accuracy. An officer who fails to observe the required 15 to 20 minute deprivation period before testing gives mouth alcohol time to contaminate the result. Radio frequency interference from police radios or cell phones has also been raised as a defense in some cases involving older devices.

There is also the human factor. Breath testing requires the subject to blow with enough force and duration for the machine to capture a deep lung air sample. If you have asthma, COPD, dentures, or simply could not seal your lips around the mouthpiece, the sample may be invalid or the machine may deliver an unreliable reading. None of these issues automatically defeat a DUI charge, but each one gives a defense attorney a legitimate avenue to question the prosecution's evidence.

The Main Ways to Challenge Breathalyzer Results

Successful challenges usually fall into a few broad categories: problems with the machine, problems with the operator, problems with the science, and problems with how the evidence was handled. A defense strategy often combines more than one of these. The stronger the combination, the harder it becomes for the prosecution to prove guilt beyond a reasonable doubt based on the breath number alone.

Machine calibration and maintenance records. Every breath testing device must be calibrated and tested on a schedule set by state law or the manufacturer. If the calibration log shows a gap, a failed accuracy check, or a repair that was never documented, the reading loses credibility. Defense attorneys routinely request these records during discovery, and in many jurisdictions they are entitled to them.

Operator training and certification. Officers must be trained and certified to administer breath tests, and their certification must be current. An expired certification, a missing refresher course, or a failure to follow the approved testing protocol can be grounds to exclude the result. Body camera footage and the incident report often reveal procedural shortcuts that the officer did not mention in the report.

Observation period violations. Most states require the officer to keep the subject under continuous observation for a set period before collecting a breath sample. The purpose is to ensure no mouth alcohol is present. If the officer looked away, answered a radio call, or allowed the subject to drink water or smoke, the required observation window is broken and the test may be invalid.

Medical and physiological factors. Conditions such as acid reflux, diabetes, low carb diets, and even recent dental work can produce trace alcohol or interfering compounds in the breath. A medical expert can explain how a person's specific health profile might cause a false high reading, and this testimony can create reasonable doubt.

Sample collection and chain of custody. Breath samples are not physical evidence in the same way blood is, but the data record, the calibration log, and the maintenance history all form a chain that the prosecution must establish. Missing records or unexplained gaps give the defense room to argue that the result cannot be trusted.

Each of these categories maps to specific motions a defense lawyer can file: a motion to suppress the breath result, a motion to exclude the officer's testimony about the result, or a request for a hearing on the reliability of the device. The right motion depends on the facts of your case and the rules in your state.

Step by Step: How to Challenge Breathalyzer Results in a DUI Case

If you are facing a DUI charge and want to question the breath evidence, the process generally follows a predictable sequence. Timing matters because there are deadlines for filing motions and requesting records. Missing those deadlines can permanently waive your ability to challenge the result. The steps below outline how a typical challenge unfolds, though the exact procedure varies by state.

1. Request discovery immediately. Your attorney will ask the prosecution for the breath test data, calibration records, maintenance logs, operator certification, and any video or audio of the traffic stop and testing. This is the foundation of any challenge.
2. Review the maintenance and calibration history. Look for gaps, failed accuracy checks, expired simulator solution, and any repair that was not followed by a proper calibration.
3. Scrutinize the officer's report and video. Compare what the officer wrote with what the video shows. Look for violations of the observation period, improper instructions, or signs that the subject did not provide a valid sample.
4. Consult a forensic toxicologist or breath testing expert. An expert can review the data and explain how machine error, physiological factors, or procedural mistakes could have inflated the reading.
5. File a motion to suppress or exclude. If the evidence is unreliable, your attorney will ask the judge to keep it out of trial. If the motion succeeds, the prosecution may have to proceed without the breath number.
6. Negotiate from a position of strength. Even if the motion is denied, the challenge often improves your bargaining position because the prosecutor knows the breath evidence is vulnerable.

This sequence is not a guarantee of any particular outcome, and no attorney can promise that a breath result will be thrown out. What the process does is force the prosecution to prove that the machine and the officer did everything correctly. When they cannot, the charge often weakens, the plea offer improves, or the case is dismissed for lack of evidence.

Common Breathalyzer Defenses Attorneys Use

Beyond the procedural steps above, defense attorneys rely on a handful of recurring arguments. The most common is the margin of error argument. Breath testing devices are typically accurate within a range of plus or minus 0.01 or more, which means a reading of 0.08 could actually reflect a true BAC of 0.07. In a borderline case, that margin alone can create reasonable doubt. Some states even require courts to instruct juries about the margin of error when the reading is close to the legal limit.

Another frequent defense is the rising blood alcohol theory. Alcohol absorbs into the bloodstream over time, so a person's BAC can continue to rise after they stop drinking. If you were stopped shortly after your last drink, your BAC at the time of driving may have been below the limit even though the test, taken 30 or 45 minutes later, showed a higher number. A toxicologist can calculate an approximate absorption curve based on your drinking timeline and body weight to support this argument.

A third defense focuses on mouth alcohol and the deprivation period. If the officer did not wait long enough, or if you burped, vomited, or used an inhaler before the test, the machine may have measured alcohol from your mouth rather than your lungs. This is one of the most technical but also one of the most effective challenges when the facts support it.

The specific defenses available in your case depend on your state's law, the type of device used, and the details of your arrest. A local DUI attorney will know which arguments judges in your courthouse tend to accept and which ones they reject. If you are not sure where to start, a service like TheLawyerDirectory can help you find attorneys in your area who handle DUI defense and breath test challenges.

What to Do Right After a DUI Arrest

The first 48 hours after a DUI arrest are critical. What you do, and what you say, can shape the entire case. You are not required to perform field sobriety tests or submit to a preliminary breath test in most states, though refusing a post arrest chemical test triggers separate license consequences. Once you are booked and released, the clock starts ticking on your right to challenge the breath result and on your driver's license suspension hearing.

Write down everything you remember while it is fresh: what you ate and drank, when you stopped drinking, any medications you take, whether you burped or vomited before the test, and how the officer conducted the stop. These details may seem trivial, but they often become the factual backbone of a suppression motion. Photograph any medical devices you use, such as an inhaler or glucose monitor, and note any medical conditions that could affect a breath reading.

Contact an attorney as soon as possible. Many DUI defense lawyers offer a free consultation and can request the breath records before they are lost or overwritten. If you are unsure whether you qualify for representation or want to compare options, you can request a free, confidential case review through a consumer matching service. AutoInjuryAccident.com is not a law firm or a lawyer referral service, and it does not provide legal advice. It connects people facing DUI or DWI charges with participating attorneys who advertise on the site. Submitting a form does not create an attorney-client relationship and does not obligate you to hire anyone.

When a Breath Test Challenge Makes Sense

Not every DUI case calls for a full scale attack on the breath evidence. If your reading was well above the legal limit and the machine records are clean, a challenge may still be worth raising but is less likely to succeed on its own. The strongest candidates for a breath challenge tend to share certain features. A reading close to 0.08, a device with calibration gaps, an officer who violated the observation period, a medical condition that affects breathing, or a stop that happened shortly after your last drink all increase the odds that a challenge will gain traction.

Even when a challenge does not eliminate the breath evidence, it can change the trajectory of the case. Prosecutors weigh risk when they decide whether to offer a plea or take a case to trial. A well documented challenge signals that the defense is prepared and that the breath number may not hold up in front of a jury. That pressure often leads to reduced charges, alternative sentencing, or diversion programs that keep a conviction off your record.

It is also worth remembering that a DUI charge involves more than the breath result. The prosecution must prove that you were in control of a vehicle, that you were impaired, and that the traffic stop was lawful. A challenge to the breath test is one piece of a broader defense strategy that may also target the stop, the field sobriety tests, and the officer's observations. An experienced attorney will evaluate all of these together rather than focusing on the breath number alone.

Key Takeaways for Anyone Facing a DUI

Breathalyzer results feel conclusive, but they are built on assumptions, procedures, and machines that can fail. Challenging those results is not about denying the obvious; it is about holding the prosecution to its burden of proof and making sure the evidence against you is actually reliable. The earlier you act, the more options you preserve.

• Breath tests estimate BAC and can be affected by calibration errors, mouth alcohol, medical conditions, and operator mistakes.
• Discovery requests for calibration logs, maintenance records, and officer certification are the foundation of any challenge.
• Motions to suppress or exclude the breath result can weaken the prosecution's case or improve a plea offer.
• Deadlines for license hearings and suppression motions are strict, so contact an attorney quickly.
• No outcome is guaranteed, but a timely, well supported challenge gives you the best chance to protect your record and your license.

If you are facing a DUI charge, do not assume the breath number ends the conversation. Gather your records, write down your timeline, and talk to a defense attorney who understands how breath testing works in your state. A free, confidential case review costs nothing and can tell you whether a challenge is worth pursuing. The sooner you start, the more room you have to build a defense.