How to Challenge a PAS Breath Test in a California DUI Case
This has to do with the preliminary alcohol screening device (PAS) related to DUI cases. Most police officers, whether they be in cars or motorcycles, will carry with them out in the field a preliminary alcohol screening device.
This is a small device used to detect whether or not somebody is under the influence of alcohol, and obviously, it's part of law enforcement's efforts to catch and convict people for DUI cases.
With my twenty-five years of experience, I can attest that the PAS device has historically had limited reliability, function, and admissibility in a criminal DUI prosecution. Understanding these limitations is crucial for anyone involved in a DUI case.
However, today, that device is used more and more, and prosecutors, with some success, are trying to get the results from the PAS device against a defendant in a DUI prosecution.
PAS Breath Test Has Issues with Accuracy
One of the device's limitations is its accuracy. Of course, having a device that can accurately measure a person's blood-alcohol level is essential in a DUI.

The problem with that device is that even the prosecutor's experts will have to testify that it has an error rate worse than the machine used at the police station.
So, the police pull somebody over and use the PAS device to make sure whether they're going to waste a trip to the police station. They use that device to see how high the blood alcohol level is.
If it's a .08 or greater or anywhere near there, they're going to arrest the person, take them in, and then put them in front of the big breath machine, which is more accurate.
In Ventura County, for example, some law enforcement agencies have a machine they use in their cars, which is pretty clever.
This is because then they get the blood alcohol much closer to the time of driving, which is a stronger argument for them if the case were to be set for trial and the defense attorney were to challenge the expert and say you're getting a breath or blood reading hours after they pull over.
How can you figure out the person's blood-alcohol level when driving?
What truly matters is the blood alcohol level at the time of driving, not hours later at the police station. This argument gains significant strength when backed by expert testimony, providing a solid defense strategy.
Challenge BAC at The Time of Driving
But this whole PAS device, now the prosecutors are trying to use the result to convict a person for a DUI, and it's one of those games where if you blow high on the PAS device and the prosecutors say, your client blew high at the time of driving.
Suppose you blow low on the PAS device and blow higher on the machine. In that case, the defense attorney says, the person was more down at the time of the driver, so it's a game back and forth between the prosecutor and the defense because a lot of times in DUI cases, law enforcement is using the PAS device, and you've got to four readings.
You have two readings from the PAS device in the field and the two reasons in the police station.
So, if all four of those are the same, the prosecutors start to have a pretty strong argument that whatever that number is, that's what your client was, and they have their experts use the results from the PAS device, the results from the breath test. Also, if the person takes blood, they will use that.
So, when you're evaluating whether you can attack this device, you certainly can. Still, the device alone will not determine whether or not somebody gets convicted of a DUI.
The device, combined with other factors, will be the final answer. In other words, how was the person driving? Did the person get in an accident?
Why were they pulled over? How did they do on the field sobriety tests? Do they have a prior criminal record for DUIs? How high was their breath result at or near the time of driving?
So, as you can see, a whole host of factors will play into whether or not somebody gets convicted of a DUI. But, indeed, understanding how the PAS device works and your defense attorney doing everything they can to use that result to your advantage makes sense in a DUI case.