DUI Laws
Breath Tests and PAS Tests in California DUI Cases
California uses two types of breath tests in DUI investigations: the roadside PAS device and the evidentiary Breathalyzer at the station. Learn how each works, their limitations, and how an attorney can challenge the results.
By Michael P. Kade — Former LAPD Officer & Criminal Defense Attorney · Updated
Educational purposes only — not legal advice. This article provides general information about California DUI law and does not create an attorney-client relationship. Consult a licensed attorney for advice specific to your situation.
Key Takeaways
- —The roadside PAS test is generally optional for drivers 21 and over not on DUI probation
- —The evidentiary breath test at the station is mandatory after a lawful DUI arrest
- —Breath machines must be regularly calibrated and maintained — records are discoverable
- —Mouth alcohol from burping, belching, or dental work can falsely inflate readings
- —GERD, acid reflux, and low-carb diets can also affect breath test accuracy
Breath testing is the most common method used to measure blood alcohol concentration in California DUI investigations. There are two distinct types of breath tests: the preliminary alcohol screening (PAS) device used roadside before arrest, and the evidentiary breath testing instrument used at the police station or jail after arrest. Understanding the difference — and the limitations of each — is fundamental to building a strong DUI defense.
The Preliminary Alcohol Screening (PAS) Test
The PAS test is administered roadside using a handheld device before a formal arrest. For drivers 21 and older who are not on DUI probation, the PAS test is voluntary — you may decline without triggering implied consent penalties. The officer is required to advise you of this right before asking you to take the test. PAS results are admissible in court as one piece of evidence, but they are generally considered less reliable than the evidentiary test administered at the station.
The Evidentiary Breath Test
After a lawful DUI arrest, you are required to submit to a chemical test. If you choose breath, the officer will administer an evidentiary breath test using a device such as the Draeger Alcotest or Intoxilyzer. California law requires the officer to observe you for a continuous 15-minute period before the test to ensure you do not burp, belch, vomit, or place anything in your mouth — all of which can introduce mouth alcohol and inflate the reading. Two separate samples must be taken within 0.02% of each other to be considered valid.
Sources of Error in Breath Testing
Breath machines measure alcohol in deep lung air and apply a partition ratio — typically 2,100:1 — to estimate blood alcohol concentration. This ratio varies significantly from person to person and can be affected by body temperature, hematocrit (the ratio of red blood cells to total blood volume), and lung conditions. Mouth alcohol from recent burping, dental work, or denture adhesives can also falsely elevate readings. Gastroesophageal reflux disease (GERD) and acid reflux can cause stomach alcohol to enter the mouth and esophagus, contaminating the breath sample.
Calibration and Maintenance Records
California law requires evidentiary breath testing instruments to be regularly calibrated and maintained. These records are public documents that your attorney can subpoena. If the machine was out of calibration, had a recent malfunction, or was not properly maintained, the results may be challenged. Defense attorneys routinely obtain the full maintenance history of the specific device used in a client's case.
Penalties at a Glance
| Offense / Situation | Potential Penalty |
|---|---|
| PAS test refusal (21+, not on probation) | No penalty — test is voluntary |
| Evidentiary breath test refusal after arrest | Implied consent violation — 1-year suspension |
| BAC 0.08%+ on evidentiary test | Per se DUI charge under VC § 23152(b) |
Penalties shown are general ranges. Actual sentences depend on the specific facts of your case.
How Attorney Kade Defends These Cases
- —Obtain the calibration and maintenance records for the specific breath machine used
- —Challenge whether the officer observed the required 15-minute pre-test period
- —Present medical evidence of GERD, acid reflux, or other conditions affecting breath readings
- —Argue that the partition ratio used does not accurately reflect the client's physiology
- —Challenge the two-sample variance if the readings differed by more than 0.02%
- —Introduce expert testimony on the limitations of breath testing technology
- —Argue mouth alcohol contamination if the observation period was not properly maintained
Frequently Asked Questions
While you are not legally required to have an attorney, a DUI conviction carries serious consequences — fines, license suspension, possible jail time, and a permanent criminal record. An experienced DUI attorney can challenge the evidence, negotiate with prosecutors, fight your DMV hearing, and potentially get charges reduced or dismissed. The cost of an attorney is almost always less than the long-term cost of a DUI conviction.
A California DUI case typically takes 3 to 12 months to resolve, depending on the county, the complexity of the case, and whether it goes to trial. Misdemeanor DUI cases in Los Angeles County often take 4 to 8 months. Felony DUI cases take longer. Your attorney can give you a more specific estimate based on the facts of your case and the court's current caseload.
After a DUI arrest: (1) Do not make any statements to police beyond identifying yourself. (2) Contact a DUI attorney as soon as possible — ideally within 24 hours. (3) Call the DMV Driver Safety Office within 10 days to request an APS hearing or your license will be automatically suspended. (4) Write down everything you remember about the stop, the tests, and the arrest while it is fresh.