A breath test result can look decisive on an arrest report, especially when the number is .08% or higher. But a proper breathalyzer accuracy review does not begin and end with that number. In a Los Angeles DUI case, the question is whether the government can establish that the device was properly used, properly maintained, and capable of producing a reliable result at the legally relevant time.
A breath result may be significant evidence. It is not automatic proof of guilt, and it should not be treated as a reason to explain, apologize, or make admissions to law enforcement. Exercise your right to remain silent and speak with counsel before discussing the stop, your alcohol consumption, or medical issues that could become evidence in the case.
What a Breathalyzer Actually Measures
California DUI cases commonly involve two very different forms of breath testing. A roadside preliminary alcohol screening device, often called a PAS device, is generally used during the investigation before arrest. A station breath test is usually administered after arrest on an evidentiary breath-testing instrument.
The distinction matters. For many drivers 21 and older who are not on DUI probation, participation in a roadside PAS test is generally voluntary. The officer may not explain that point clearly in a stressful roadside encounter. Different rules can apply to drivers under 21 and people on DUI probation.
After a lawful DUI arrest, California’s implied-consent law generally requires a person to submit to a chemical test. Refusing a post-arrest test can create separate consequences and may be used by the prosecution. Do not make that decision based on a general article or an officer’s pressure. The immediate priority after an arrest is to avoid discussing the facts and obtain specific legal advice as soon as possible.
Neither type of device measures alcohol in a person’s blood directly. It measures alcohol in deep-lung breath and uses a mathematical assumption to estimate blood alcohol concentration. That process can be reliable when the protocol is followed. It also creates factual and technical issues that a defense investigation should examine rather than assume away.
Breathalyzer Accuracy Review: The Evidence That Matters
A meaningful review starts with the entire chain of events, not just the final printout. In Los Angeles County, the arresting officer’s report often provides a compressed version of the traffic stop, field sobriety exercises, PAS test, arrest, observation period, and evidentiary test. Video and underlying records may tell a more complete story.
California regulations govern how evidentiary breath tests are administered. Among other matters, the prosecution must be able to establish that the operator followed required procedures and that the instrument was functioning within applicable standards. A defense review may focus on the observation period before testing, whether the person placed anything in their mouth, whether there was vomiting or regurgitation, the quality and timing of the breath samples, and whether the two reported samples were sufficiently consistent.
The instrument’s records also matter. Maintenance, accuracy-check, calibration, repair, and error records can show whether the device was properly maintained or whether there were recurring problems. A machine can be approved for use and still be improperly operated on a particular night. A clean-looking printout does not answer every foundational question.
The timing issue is often central. California Vehicle Code section 23152(b) concerns driving with a blood alcohol concentration of .08% or more. A test at the station may occur well after driving stopped. If alcohol was still being absorbed, the result at the time of testing may not reliably show the alcohol concentration while the person was driving. This is often called a rising-blood-alcohol issue. It requires careful analysis of timing, claimed drinking history, food consumption, test results, and the prosecution’s available evidence. It is not a defense that should be casually asserted without supporting facts.
Medical and Physical Factors Are Not Automatic Defenses
People often hear that acid reflux, diabetes, mouthwash, dental work, or certain diets can defeat a breath test. The reality is more limited. A medical condition or substance only matters if it plausibly affected the particular test and can be supported through records, expert analysis, reliable testimony, or weaknesses in the testing procedure.
For example, residual mouth alcohol can interfere with a breath result if alcohol from the mouth, rather than deep-lung air, affects the sample. That is one reason the pre-test observation protocol is important. But claiming reflux after an arrest is not enough by itself. The defense needs to determine what happened during the observation period, what the video shows, whether the person reported symptoms, and whether medical history supports the issue.
Breathing pattern can also affect a result. The length and force of a breath sample, hyperventilation, breath-holding, or difficulty providing a proper sample can raise questions in an appropriate case. These are technical matters. They should be evaluated alongside the device data, not presented as generic talking points.
Roadside Testing Can Affect the Entire Case
An officer’s decision to stop a vehicle and conduct a DUI investigation is not beyond review. A breath result does not erase problems with the original traffic stop, the prolonged detention, or the arrest itself.
The defense may examine the stated basis for the stop, dispatch information, body-worn camera footage, dash camera footage, the officer’s observations, and the conditions under which field sobriety tests were performed. Uneven pavement, poor lighting, footwear, fatigue, injury, anxiety, language barriers, and unclear instructions can affect roadside performance. Those issues may not directly alter a later breath number, but they can affect whether the officer had a lawful basis to expand the encounter, request tests, or make an arrest.
If a constitutional violation occurred, counsel may seek to suppress evidence through a motion. The consequences depend on the facts and the procedural posture of the case. Suppression litigation is not a formality. It requires early preservation of video, reports, dispatch records, and witness evidence before material is lost or overwritten.
A High Breath Result Does Not End the Defense
California courts generally permit the prosecution to rely on properly administered evidentiary breath testing. The published decision in People v. Vangelder places limits on broad attacks claiming that approved breath devices are inherently unreliable in every case. That does not prevent a focused challenge to the actual testing process, the foundational records, the timing of the test, an officer’s observations, or whether the government can prove the required elements beyond a reasonable doubt.
It also matters which charge the prosecutor is pursuing. A .08% or higher breath result is particularly relevant to the per se DUI allegation under section 23152(b). A separate allegation under section 23152(a), driving while under the influence, turns on impairment. Conversely, a result below .08% does not automatically eliminate an impairment-based DUI charge. The evidence must be analyzed charge by charge.
In some cases, the strongest defense is technical. In others, it is the lack of reliable impairment evidence, a flawed stop, a disputed driving timeline, or a problem with how the test was obtained. The right strategy comes from the evidence, not from a one-size-fits-all challenge to every breath machine.
What to Preserve and What to Avoid
After a DUI arrest, do not post about the incident, contact potential witnesses to coordinate accounts, or try to recreate your drinking timeline from memory in text messages. Do not assume the officer’s report is the complete record, either.
Write down what you personally remember while it is fresh: when you last drove, when you were stopped, when each test occurred, what you ate or drank, whether you burped or felt ill, what the officer said, and whether cameras were present. Keep receipts, rideshare records, restaurant records, and medical information that may establish a reliable timeline. Then give that information to your attorney rather than trying to argue the case with police or prosecutors.
A breath result deserves a disciplined review before a plea decision, DMV hearing, preliminary hearing, or trial preparation. If you were arrested in North Hollywood, Los Angeles, the San Fernando Valley, elsewhere in Los Angeles County, or anywhere in Southern California, contact Wegman & Levin APC at (818) 495-8330 for a confidential consultation. Early review can preserve the records needed to determine whether the breath evidence actually supports the charge.
