I am Joel Brand, and I defend DUI cases throughout California. One of the first things a client tells me when they call is their breathalyzer number. They say it quietly, like a verdict. In this post I want to explain what that number actually represents, what it does not represent, and why it is rarely the end of the conversation it feels like in the hours after an arrest.
The Number You Saw May Not Be the Number That Counts
Many people arrested for DUI in California remember a number from a roadside device called a preliminary alcohol screening, or PAS, test. That handheld instrument is different from the evidentiary breath test given at the station. California courts treat those two readings very differently. The PAS result is used to establish probable cause for the arrest. The evidentiary test taken later is what prosecutors actually rely on at trial. If your roadside number was, say, 0.09 and your station result came in differently, that gap matters. You can read more about how those two tests compare in the library article on driving with a BAC of 0.08 percent under VC 23152(b).
What 0.08 Percent Actually Means Scientifically
A blood alcohol concentration of 0.08 percent means that eight one-hundredths of one percent of your blood volume is alcohol. That is a very small quantity. Breath testing machines do not measure blood directly. They measure alcohol vapor in deep lung air and then apply a conversion formula to estimate what is in your blood. That conversion assumes a breath-to-blood ratio of 2100 to 1. Every human body is different. People whose actual ratio is closer to 1700 to 1 will consistently produce a breath reading that overstates their true BAC. That is not a technicality. It is a documented physiological variable that a defense attorney can raise.
Instrument Calibration and Maintenance Records
Breath testing machines must be calibrated and maintained on a regular schedule under California regulations. When a machine drifts out of tolerance and has not been properly serviced, every reading it produces during that period is suspect. As part of building a defense, I routinely request calibration logs and maintenance records for the specific instrument used in my client's case. A poorly maintained machine is a real issue, not a loophole. The bad calibration defense has a legitimate scientific foundation.
The Rising BAC Problem
Alcohol does not instantly flood your bloodstream the moment you swallow a drink. It absorbs over time, typically between 30 minutes and 90 minutes depending on many factors including food intake, body weight, and the type of beverage. If you were still absorbing alcohol at the time you were driving, your BAC at the wheel may have been lower than the number the machine captured 30 or 45 minutes later at the station. This is called the rising BAC defense, and it is one of the more scientifically grounded arguments available in a California DUI case. You can read a fuller explanation in the library article on the rising BAC defense.
Mouth Alcohol and Why It Distorts the Reading
Breath testing machines are supposed to sample deep alveolar air from the lungs. If there is residual alcohol in your mouth from a recent drink, a burp, acid reflux, or a dental device, the machine can pick up that mouth alcohol instead of or in addition to lung air. The result is an artificially inflated number. Officers are supposed to observe you for 15 minutes before administering the test to prevent exactly this problem. If that observation period was skipped or was not continuous, the reading may be challenged under the mouth alcohol defense. Separately, if you have a condition like GERD, that can cause ongoing reflux of alcohol-laden stomach contents into the mouth, which compounds the problem.
A High Number Is Not Automatically Fatal to Your Case
If your reading was significantly above 0.08, you may feel as though there is nothing to argue. That is understandable, but it is not accurate. Even at elevated readings, the issues described above still apply. Beyond that, the prosecution still has to prove that you were the person driving, that you were driving on a public road, and that the test was properly administered and the chain of custody preserved. Cases with readings of 0.15 or higher carry a high BAC sentencing enhancement, which makes it even more important to examine every procedural step carefully rather than accepting the number at face value.
The Difference Between 0.08 and a Drug DUI
California has two separate DUI charges. One is based purely on your BAC under VC 23152(b). The other, under VC 23152(a), is based on whether you were actually impaired, regardless of your precise number. A person can be charged under 23152(a) even if their BAC tested below 0.08, if the officer's observations suggest impairment. Conversely, a person with a BAC just above 0.08 who drove perfectly and passed most field sobriety tests may have a stronger argument under 23152(a) than the raw number suggests.
What Happens to That Number at the DMV
Your breathalyzer result does not just follow you into criminal court. The DMV uses it in a completely separate administrative proceeding that can suspend your license before you ever set foot in a courtroom. The administrative per se suspension process is governed by VC 13353.2, and challenging it at a DMV hearing requires a different strategy than your criminal defense. The two tracks run in parallel, and the breath test result is central to both. Understanding how to prepare for the DMV hearing is one of the first things I walk every new client through.
What the Officer Wrote Down About Your Test
The arresting officer fills out a form called a DS-367 at the time of the arrest. That form records, among other things, the breath test results, the observation period, and which instrument was used. Errors or omissions on that form can open doors in your defense. I cover the most significant ones in the library article on DS-367 mistakes that can help your DUI case. Ask your attorney to pull that document and review it carefully.
Your Number and the Possibility of a Reduced Charge
One outcome that comes up in cases with borderline readings is a reduction to a wet reckless, which is a charge under VC 23103.5. Prosecutors sometimes offer this when the evidence has exploitable weaknesses, including questions about the breath result. A wet reckless carries significantly lower penalties and does not trigger the same licensing consequences as a DUI conviction. Whether that offer materializes depends on the specific facts of your case, the county, and how the evidence holds up to scrutiny. It is worth understanding what factors influence a wet reckless offer before your first court date.
The Number Is a Starting Point, Not a Sentence
I have handled DUI cases across California long enough to know that a breathalyzer reading is a piece of evidence, not a verdict. It was produced by a machine, recorded by a human, and subjected to conditions that may or may not have been ideal. It can be tested, questioned, and sometimes undermined. The most important thing you can do right now is not accept it as the final word before anyone has examined how it was obtained.
If you want a free written analysis of your case, including what questions I would ask about your breath test, you can request one right here on this page. You can also call me directly at (888) 271-6644. I answer my own phone, 24/7. For more articles on what to expect after a California DUI arrest, visit more from the DUI blog.