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A Tale of Two Breath Tests

By on Jan 15, 2015 | 3 comments

There are two breath tests.

Does that sound simple? Many, many drivers across Washington make a mistake when stopped by the police because they do not realize there are two breath tests. Some of my clients are among those people, and my job gets a lot harder when they treat one breath test like the other. So today let’s put the ambiguity to bed and explain the differences between the two breath tests.

There are a lot of differences between the tests, including purpose and technology, as I’ll get into a moment. But the easiest way to tell them apart is simply to look where the particular test is being administered. Is a test being administered on the side of the road via handheld device? That’s the PBT. Have you been transported to a police station and are blowing into a larger machine? That’s the DataMaster.


The PBT stands for “Preliminary Breath Test” (although it’s often referred to, even by police, as the “portable breath test.”) The PBT is a handheld device that police carry with them to determine your breath alcohol concentration on the side of the road (but more about that in a second). It looks like this:


The use of the PBT is approved by statute but there are a lot of rules and restrictions on its use. The important one is here and because it says lots of interesting things, I’ll unpack it a bit.

The first is that the sole purpose of the PBT is to establish probable cause to arrest. Probable cause, defined essentially as a reasonable belief that a crime has occurred, is the prerequisite to a lot of other things like obtaining warrants and arresting people. A defendant is very happy when there is no probable cause to do X, where X is the action the police officer took (or wants to take). The probable cause requirement is what keeps police from arresting people for any reason or no reason. There has to be some basis, and that basis is what the courts call probable cause.

Because the PBT is only used to establish probable cause, it is not admissible for any other purpose. The results can be admitted at a hearing if probable cause is challenged, but it cannot be admitted to help a jury determine whether someone is actually guilty. Despite the language in the rules saying how accurate it is, it produces erroneous readings all the time. Often enough the legislature has determined it is not reliable enough to be considered as evidence of guilt or innocence.

Interestingly the rule also says the PBT, by itself, is not enough to establish probable cause to arrest. That means if a driver is taking a PBT and it comes back something outrageous like .6, that alone is not enough for an officer to arrest. Well the driver would be dead anyway, but that’s besides the point. However that little rule rarely, if ever, comes up. For one, the officer stopped you because you probably committed some traffic infraction like speeding or forgetting to turn on your headlights. Bad driving + bad PBT = probable cause to arrest. In addition, every officer in the world writes in their report “the driver had bloodshot, watery eyes and I could smell the odor of intoxicants.” Looking and smelling drunk + bad PBT = probable cause to arrest.

The final sentence of the linked rule has two big parts. The first says the test is voluntary and the second is that taking it, or not, doesn’t matter for the implied consent statute. We’ll get to the implied consent statute in a second but for the PBT that word “voluntary” is…important.

In short there’s very little incentive to take a PBT, and because it’s voluntary there’s very little penalty if you don’t. Here’s the very little incentive to take it: If you’re stopped at the road and are 100% sure you haven’t been drinking, some lawyers advocate for taking the PBT to let the cop know you’re ok to drive and to get sent on your way. As I wrote about my own experiences with being pulled over, I took the PBT. Presumably it was 0.00 or very close to it and I was let go. Perhaps because I was so friendly and cooperative, I even got out of there without receiving a ticket. And that’s the minor penalty, police don’t like be opposed so they may give you that ticket, or even arrest you, for not being compliant.

But as I’ve said before, the goal of a police interaction is not to avoid being arrested, but to avoid being convicted of a crime. The PBT is used to establish probable cause. And as I noted above, police need probable cause or the arrest was unlawful. And if the arrest was unlawful, everything that comes after that gets thrown out. Which means without probable cause, a defendant will never be convicted of a crime.

Because of that I will almost always recommend a person decline to blow into the PBT. Admittedly a 0.00 reading is a good thing to get, but if you’ve been near alcohol that day, it’s a big risk. And the little machines really are imperfect. While a competent lawyer could challenge the results later, why even expose yourself to that? PBTs can be declined without any penalty, and they should be.

The DataMaster

 Things get more complex when a DataMaster is involved. That’s because if you’ve been transported to the station for this breath test, you are already under arrest.  

The DataMaster is a much larger machine at a table, with tubes and spectrometry and other indicia of reliability. The legislature has determined that if the protocols are followed, the results are admissible in a trial. The DataMaster looks like this:

Unlike the PBT, refusing to take the breath test at the station does have penalties. Those penalties are based around Washington’s “implied consent” statute. The statute states as a condition to be granted the privilege to drive in this state, every driver implicitly consents to having their breath taken, when the officer has probable cause to believe the driver committed a DUI-type crime. That consent can be withdrawn, but not without penalties.

There are two and a half penalties for refusing to take a breath test. The first is that upon a refusal the driver’s license is automatically revoked for one year. The second penalty is that the refusal is admissible in a criminal trial, such that the prosecutor can argue the driver refused to blow because the driver knew he or she would be over the legal limit. And the half penalty? The police can obtain a warrant to take a driver’s blood to test for alcohol content.

The warrant creates the double whammy of all the penalties of a refusal without the presumed benefits. Plus no one wants their blood forcibly extracted. However, not every refusal results in a warrant. The officer has discretion, and in my experience, they exercise it based on how busy they are and how serious the alleged DUI is (for example, a DUI involving an accident is more likely to trigger requesting a warrant than a driver being stopped because of an illegal lane change).

So should you take or refuse the DataMaster? The question is incredibly fact-specific, so much so it would be unethical to even try to answer it here. Because the DataMaster only comes into play when someone is arrested, that person has additional rights. In fact before the DataMaster is even used, the driver has to be told they have the right to contact an attorney. And I strongly recommend anyone in this situation do so. I hope it never comes up for you but if it does, request to talk to an attorney before deciding whether to blow or refuse. 

Finally, the DataMaster is an extremely old machine. It’s well out of warranty and are no longer being manufactured. The Washington State Patrol, noting the difficulty in maintaining such old technology, is replacing all the DataMasters in the state with the Draeger machine. Is it more reliable? Only time will tell.

People get confused by the two breath tests in Washington. The important thing to remember is they serve different functions and carry different risks for Washington drivers. It’s also crucial to know you may be entitled to an attorney, and if are entitled you should request one as soon as possible. If you or someone you know should need a DUI attorney, feel free to give me a call.

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  • Travis

    Won’t refusing a PBT lead to an arrest so they can get you to use the DataMaster?

  • Mark Conkle

    As Noah stated, that is possible, but far from guaranteed. However, as he reminds you, being arrested is a minor inconvenience when compared to being convicted of a crime. By not taking the PBT, the office has less probable cause to arrest you, which could work in your favor even if you are arrested. “A defendant is very happy when there is no probable cause.”

    Particularly if you expect the PBT will not result in your favor, there is no reason to take it. As Noah says, if you have not been drinking lawyers disagree about whether you should take the PBT anyway. It is not a reliable device and there is no legal incentive to taking it. It will never be used in your favor.

  • John

    If the difference between PBT .114 and Datamaster .08 is ~30% (.034) doesn’t that indicate some problem with accuracy of the test of one of them?

The facts and circumstances of your case may differ from the matters in which results and testimonials have been provided. Every case is different, and each client’s case must be evaluated and handled on its own merits.