I am Joel Brand, a California DUI defense attorney, and in this post I want to address a question I hear often from people who were just arrested: what happens when you believe the officer recorded your blood alcohol level incorrectly at the scene? Maybe the number seemed impossibly high. Maybe the device looked questionable. Maybe you were given one reading on the roadside and a different one later. Whatever the reason, the BAC figure the officer wrote in his report is not automatically the final, unchallengeable truth about your case.
The Roadside PAS Device Is Not the Evidentiary Test
California law draws a clear line between the handheld preliminary alcohol screening device used at the roadside and the evidentiary chemical test administered after arrest. The roadside device, called a PAS or preliminary alcohol screening test, is a field investigation tool. It is not the official measurement that the prosecution relies on at trial. The evidentiary breath or blood test comes later, either at the station or, in some cases, at a hospital. If you believe the officer quoted you a roadside number that does not match your actual condition, you should know that the law already treats that number differently from the official result. You can read more about how these two tests differ in the library article on chemical test refusal under VC 23612.
Why the Evidentiary Result Can Also Be Wrong
Even the official evidentiary test can be inaccurate. Breath machines must be calibrated on a regular schedule, and a machine that has fallen out of calibration can produce results that are higher than your true BAC. This is sometimes called the bad calibration defense, and it is one of the most fact-intensive defenses available in California DUI cases. If the machine used on you had not been properly maintained, the recorded number may not reflect what was actually in your blood at the time of driving.
Mouth Alcohol Can Inflate the Reading
Breath machines are supposed to measure deep lung air. If you had recently burped, vomited, used mouthwash, or had a dental condition that trapped residual alcohol in your mouth, the sensor may have captured that surface alcohol rather than the alcohol in your blood. The result is an artificially elevated reading. This is the mouth alcohol defense, and it applies even when you were not attempting to deceive anyone. Officers are supposed to observe you for fifteen minutes before administering a breath test to guard against exactly this problem. If that observation period was skipped or abbreviated, the result may be challengeable.
The Rising BAC Theory Matters Too
Alcohol takes time to absorb into the bloodstream. If you had your last drink shortly before you drove, your BAC may have still been climbing when you got behind the wheel and then peaked by the time the officer tested you. This means the number on the test could be higher than what was in your blood while you were actually driving, which is the moment that matters legally. The rising BAC defense is a legitimate scientific argument that a qualified expert can present in your case.
How Blood Test Results Can Go Wrong
If you chose the blood test or were taken to a hospital, the sample itself can be a source of error. Blood samples must be stored, handled, and analyzed according to strict protocols. Fermentation inside a poorly preserved tube can cause the alcohol content to increase after the blood was drawn. Chain of custody gaps, contaminated tubes, and lab technician error are all documented problems in California DUI cases. If any of these issues exist in your case, the reported number may not reflect reality.
What the Police Report Actually Says and Why It Matters
The officer's report is the foundation of the prosecution's case, but it is also a document full of potential errors. Officers record their observations under pressure and sometimes fill in details incorrectly. The number they write for your BAC, the time of the test, the device used, and the observation period are all facts that your attorney will scrutinize. Understanding common police mistakes at a DUI stop is one of the first things I do when I take a new case.
The DS-367 Form and What It Tells You
When you were arrested, you should have received a pink temporary license and a form called the DS-367. That form contains important information about how the chemical test was administered. Errors or inconsistencies on the DS-367 can support a challenge to the reported BAC. There is a detailed breakdown of DS-367 mistakes that can help your DUI case in the library if you want to understand what to look for.
You Have a Right to an Independent Test
California law gives you the right to obtain an independent chemical test after you submit to the official evidentiary test. If you requested one and were denied, or if the officer failed to inform you of that right, that is a procedural violation that may affect how the evidence is treated. An independent result that differs significantly from the official result is powerful evidence that something went wrong in the testing process.
What a Motion to Suppress Can Accomplish
If the BAC evidence was obtained through an unlawful stop, an unlawful detention, or a testing procedure that violated your rights, I can file a motion to suppress evidence under Penal Code 1538.5. If that motion succeeds, the prosecution may lose its primary evidence, which changes the trajectory of the entire case. This is not a guarantee of any particular outcome, but it is a tool that an experienced DUI attorney knows how to use.
Acting Quickly Protects Your Ability to Challenge the Evidence
Evidence does not last forever. Breath machine calibration logs, maintenance records, and surveillance footage from the arrest location all have limited windows before they are overwritten, recycled, or destroyed. The sooner your attorney submits preservation demands and begins gathering records, the better positioned you are to challenge a BAC result that may be wrong. You should also be aware that the DMV and the court are two separate proceedings with separate deadlines, as explained in the article on the first ten days after a DUI.
A Wrong BAC Number Does Not Have to Define Your Case
If you believe the number the officer recorded does not reflect your true condition that night, you are not imagining things. These errors happen, and California DUI law provides real mechanisms for challenging them. The defenses I have described here are fact-specific. Whether any of them applies to your situation depends on the details of your arrest, the equipment used, and the procedures the officer followed. That is exactly the kind of analysis I provide when I review a case. I also encourage you to read about the full range of California DUI defenses and about what a first-time DUI conviction means legally so you understand what is at stake.
You can get a free written case analysis right here on this page. Call me at (888) 271-6644. I answer my own phone, 24/7. And if you want to read more about defending a California DUI, visit more from the DUI blog.