I am Joel Brand, and I defend DUI cases across California. If you recently took a breath test after a DUI arrest, you may have heard about something called the 15 minute observation period. This is one of the most important procedural rules in California DUI law, and it is also one of the most common areas where officers make mistakes. In this post, I will explain what the observation period is, why it matters, and how a failure to follow it can affect your case.
What Is the 15 Minute Observation Period
Under California Title 17, an officer must observe you continuously for roughly 15 minutes before administering an evidentiary breath test. The purpose is to make sure you do not burp, regurgitate, or have anything in your mouth that could contaminate the breath sample. The goal is to ensure the machine is measuring deep lung air rather than alcohol lingering in your mouth.
Why Mouth Alcohol Is a Problem
Breath testing machines are designed to measure alcohol from deep in your lungs. When alcohol remains in your mouth, from dental work, food particles, or stomach contents that come back up, the machine can read a falsely high number. This is called mouth alcohol contamination. The 15 minute observation period exists to give enough time for any mouth alcohol to dissipate so the breath test result is reliable.
What the Officer Must Do During Observation
The officer does not need to stare directly at your face without blinking for 15 minutes. However, the officer must maintain continuous observation of you. This means the officer should be watching for any burping, belching, regurgitation, or anything going into your mouth. If any of those things happen, the observation period should start over. The officer should also make sure you do not put anything in your mouth during this time.
Continuous Versus Intermittent Observation
Title 17 calls for continuous observation. This does not mean the officer cannot look away briefly, but the observation should not be broken up into scattered intervals. If the officer walks away, steps outside, talks on the phone, or gets distracted by paperwork for several minutes, the continuity is broken. Intermittent observation is not the same as continuous observation, and a break in continuity can be grounds to challenge the breath result.
Common Mistakes Officers Make
Officers are human and they get busy. I have seen cases where the officer started the observation period but then left the room. I have seen cases where the officer was doing paperwork, answering the radio, or talking to another officer. Sometimes the officer claims 15 minutes passed but the video or audio shows otherwise. These are all things I look for when reviewing a case.
How the Observation Period Is Documented
Officers typically note the observation period in their report. Some agencies use a specific form. Some dashcam or bodycam systems capture at least part of the observation. The evidence in your case may include the officer's written report, audio recordings, video footage, and the breath test log. All of these sources can help determine whether the observation was done correctly.
What Happens If the Observation Was Not Done Properly
If the officer did not properly observe you for the required period, the reliability of the breath test can be challenged. This does not mean the case is automatically dismissed, but it gives me leverage. I can file motions to suppress the breath result or argue to a jury that the number is not trustworthy. A successful challenge can significantly change the trajectory of your case. For more context, see the top DUI defenses.
The Difference Between Breath and Blood Tests
The 15 minute observation rule applies to breath tests, not blood tests. A blood draw does not require an observation period because the sample comes directly from your bloodstream. This is one reason blood tests are generally considered more reliable than breath tests. However, blood tests have their own potential issues, such as chain of custody problems or fermentation of the sample. Each type of test has its own set of defenses.
How This Connects to Your DMV Hearing
The DMV hearing is separate from the criminal court case, and both can be affected by observation problems. At the DMV hearing, the burden is on the DMV to show the breath test was reliable. If the observation was flawed, I can argue the DMV has not met its burden. You have a limited time to request this hearing, so it is important to act quickly. Learn more in how the DMV hearing works and the first 10 days after a DUI.
How This Affects Your License
A breath test result that gets suppressed or called into question can affect what happens to your driver license. If the DMV cannot rely on the breath result, it may not be able to sustain a license suspension. This is one reason why the observation period matters beyond the courtroom. For a broader overview, read how a DUI affects your license.
How This Fits Into the Court Process
In criminal court, the prosecutor needs evidence to prove you were driving under the influence. The breath test is often their strongest evidence. If I can challenge the breath result based on a faulty observation, the prosecutor's case gets weaker. This can open the door to reduced charges or even dismissal. To understand the full timeline, see the DUI court process step by step.
Potential Outcomes When the Breath Test Is Challenged
Every case is different, and outcomes are always fact-specific. I cannot promise a particular result. However, when a breath test is successfully challenged, the possibilities can include suppression of the evidence, reduction of charges, or a not guilty verdict at trial. The strength of the challenge depends on the facts of your stop, the officer's conduct, and the available evidence. For more perspective, see how DUI cases get dismissed or reduced.
Why You Need Someone Reviewing the Details
The observation period is just one piece of the puzzle. There are many other details in a DUI case that need careful review, from the reason for the stop to the field sobriety tests to the calibration of the breath machine. This is why having someone who knows what to look for matters. I review every detail because small procedural errors can make a big difference. For a wider view, check out the broader California DUI defenses guide.
What You Should Do Now
If you were arrested for a DUI and took a breath test, the most important thing is to act quickly. Evidence can disappear, video can be overwritten, and deadlines pass. You have a limited window to request a DMV hearing. The sooner I can start reviewing your case, the sooner I can identify issues like a faulty observation period. Read about the consequences of a first DUI and the California DUI penalties guide to understand what is at stake.
I offer a free written case analysis on this page. Call me at (888) 271-6644. I answer my own phone, 24/7. You can also read more from the DUI blog.