US Supreme Court Declines to Hear Breathalyzer Challenge

The U.S. Supreme Court recently declined to hear an appeal challenging the accuracy of a breathalyzer in a California DUI case. The appeal came out of a California Supreme Court decision holding that a DUI defendant couldn’t have his expert witness testify that the breathalyzer machines used in California were unreliable. Because there has always been a lot of confusion surrounding breathalyzer machines, let’s talk about what this court decision does and doesn’t mean.

Does this mean the U.S. Supreme Court upheld the use of breathalyzer machines?

No. All this decision means is that the U.S. Supreme Court, for whatever reason, decided it didn’t want to review the decision of the California Supreme Court. It did this without publishing any opinion saying why it did this.

The case, Vangelder v. California, was appealed to the U.S. Supreme Court on what’s called a Petition for a Writ of Certiorari. This is basically a request for the Court to hear the case even though it doesn’t have to do so. The Court has also explained before that its decision to not grant a Writ of Certiorari has no bearing “on the merits of the case.” Missouri v. Jenkins, 515 U.S. 70 (1995). So basically the Court’s decision means nothing outside of California. Keep in mind, though, that states besides California can look at the California court’s decision for guidance in making future legal decisions about breathalyzer machines (this is what attorneys call “persuasive authority”).

What did the California case actually say?

At the state court level, the defendant (Vangelder) was trying to have an expert testify in his DUI case that the way the breathalyzer machines work (specifically the “partition ratio variability” factor, if you were curious) causes them to be unreliable. The trial court prevented Vangelder from presenting this testimony, and Vangelder appealed. The California Supreme Court held that the trial court did not err in preventing the defendant’s expert on breathalyzer machines from testifying that they are inherently unreliable, due to prior decisions upholding their use as well as scientific consensus that they are fairly accurate.

Does this case mean breathalyzer results can’t be challenged?

No. Let’s make a distinction here before going any further. There are two basic ways of saying a breathalyzer result is wrong or is unreliable:

  1. All breathalyzer machines are unreliable.
  2. The specific breathalyzer machine used in my arrest is unreliable.

See the distinction?

For number 1, this California case only applies to California, so as far as cases there go it looks like the courts are going to uphold the reliability of breathalyzer machines in general. In Florida, police use the Intoxilyzer 8000 machine, which is still being challenged in the courts.

For number 2, the results of an individual breathalyzer can still be challenged if the breathalyzer was malfunctioning, had not been serviced properly, had not been properly calibrated, and so forth. Breathalyzer machines must be properly maintained and serviced, and must be sent to the Florida Department of Law Enforcement at regularly scheduled intervals for calibration and testing in order for the results to be valid. These are issues that your attorney will investigate.


The U.S. Supreme Court’s decline of the appeal in this case doesn’t mean all breathalyzer results are now set in stone. If you’ve been arrested for a DUI and gave a breath sample talk to an attorney about what your options are.