How Reliable Are Handheld Breathalyzer Tests in Arizona DUI Cases?
If you were stopped for suspected DUI in Tucson, an officer may have asked you to blow into a small handheld device on the side of the road. The officer may even have told you that you were “over the legal limit.”
For many people, that sounds like the end of the case.
It isn't.
One of the first questions a DUI defense attorney should ask is what kind of breath test was actually administered, when it was administered, and what the government is trying to prove with the result.
A handheld roadside breath test—often called a preliminary breath test (PBT)—is not necessarily the same thing as the chemical breath testing used to establish a person's alcohol concentration in a DUI prosecution. And even when a device produces a numerical result, that number needs to be understood in context.
If you were arrested for DUI in Tucson or Pima County after taking a handheld breath test, here is what you should know.
What Is a Handheld Breathalyzer or Preliminary Breath Test?
During a DUI investigation, an officer may use a portable breath-testing device to obtain an estimate of the amount of alcohol in a driver's breath.
People commonly refer to these devices as “breathalyzers,” although that term can cause confusion because there are different types of breath-testing equipment used during DUI investigations.
A handheld PBT is generally used during the roadside investigation. It may be considered along with other information the officer has gathered, such as:
the reason for the traffic stop;
driving behavior;
the odor of alcohol;
statements about drinking;
observations of speech, balance, or coordination;
performance on field sobriety tests; and
other circumstances surrounding the investigation.
The important point is that a roadside breath test is one piece of evidence.
A DUI case should not be evaluated simply by asking, “What number did you blow?”
A Roadside PBT Is Not Necessarily the Same as an Evidentiary Breath Test
This distinction is important.
After a DUI arrest, Arizona law provides procedures for chemical testing of a driver's blood, breath, urine, or other bodily substance under certain circumstances. That testing can have consequences both in the criminal DUI case and in separate proceedings involving driving privileges.
That is different from simply being asked during a roadside investigation to blow into a small handheld device.
Unfortunately, people understandably describe both as “the breathalyzer.”
A client might tell me:
“I took the breathalyzer and blew a .10.”
Before drawing conclusions from that statement, I want to know much more.
Was this a small handheld device on the side of the road? Was another breath test performed later? Was blood ultimately drawn? How much time passed between driving and each test? What did the officer say before administering the test? What does the police report say? What does the body-camera footage show?
Those details matter.
How Reliable Are Handheld Breathalyzer Tests?
Handheld breath-testing devices can provide useful information, but no scientific instrument should be treated as magically infallible.
A breath-test result depends on both the instrument and the circumstances under which the sample was obtained.
Potential issues can include the following.
1. Calibration and Maintenance
A measuring instrument needs to function properly.
Depending on the particular device and the purpose for which the government seeks to use its result, records concerning calibration, accuracy checks, maintenance, and device performance may become important.
If the State wants a court or jury to rely on a number produced by a machine, a defense attorney should consider whether there is an adequate foundation for that result.
2. Residual Alcohol in the Mouth
Breath-alcohol testing is intended to obtain information related to alcohol in a person's breath—not simply detect alcohol that happens to remain in the mouth.
Recently consuming an alcoholic beverage can therefore be significant.
Other circumstances involving alcohol in or around the mouth may also need to be considered depending on the facts of the case and the testing device involved.
That is one reason the timing and circumstances surrounding a breath sample matter.
3. Testing Procedure
Even a properly functioning device must be used appropriately.
Questions may include:
Who administered the test?
Was that person trained to use the particular device?
Were the manufacturer's or agency's procedures followed?
How long had it been since the person's last drink?
What happened immediately before the test?
Was the device functioning normally?
Were there error messages or repeated attempts?
Is the officer's description consistent with the body-camera footage?
The number should not be separated from the process that produced it.
4. Timing
Alcohol concentration changes over time.
A breath result obtained at one point does not automatically establish a person's alcohol concentration at an earlier point.
Suppose an officer believes a person was driving at 11:30 p.m., but a breath sample is obtained later. Depending on the circumstances, the person's alcohol concentration could have been increasing, decreasing, or near its peak during the intervening period.
That can become particularly important when someone consumed alcohol shortly before driving.
If the PBT Says I'm Over .08, Doesn't That Prove DUI?
Not by itself.
Arizona DUI law is more complicated than the familiar phrase “the legal limit is .08.”
Arizona has different DUI theories, including driving or being in actual physical control of a vehicle while impaired to the slightest degree and having an alcohol concentration of .08 or more within the statutorily defined period under the circumstances specified by Arizona law.
Those are legal allegations the State must prove. A roadside number does not eliminate those requirements.
There may also be significant factual questions about when the person drove.
For example, police sometimes encounter someone after driving has already ended. An officer may not have personally observed the person driving at all.
That creates additional questions:
When was the vehicle actually driven? When was alcohol consumed? How much time passed before police arrived? Could the person have consumed alcohol after driving? What evidence establishes the relevant timeline?
In DUI defense, time matters.
What If My Handheld Breath Test and Blood Test Don't Match?
This is another reason not to evaluate a DUI case based on one roadside number.
If multiple tests were performed at different times, the results need to be considered in relation to the timeline.
Alcohol is absorbed into the bloodstream and later eliminated from the body. Consequently, a person's alcohol concentration is not necessarily identical throughout an evening.
A later blood result, for example, does not automatically tell us the person's exact alcohol concentration at an earlier moment without additional assumptions and analysis.
The same is true when comparing a roadside breath result with a later chemical test.
A difference between results does not automatically prove that one test is “wrong.” Instead, it raises questions about timing, absorption, elimination, testing methods, and the factual circumstances of the case.
What Is the Widmark Formula?
In some DUI cases, alcohol calculations may be used to estimate alcohol concentration based on factors such as alcohol consumption, body weight, distribution of alcohol within the body, and the passage of time.
These calculations are commonly associated with the Widmark formula.
At first glance, this can sound extremely precise: plug numbers into a formula and determine someone's BAC.
Human beings, however, are not calculators.
A Widmark calculation depends on inputs and assumptions. Those assumptions can include the amount of alcohol actually consumed, the alcohol content of the beverages, when the drinks were consumed, body characteristics, absorption, and elimination.
Change an assumption and you may change the estimate.
That doesn't make alcohol calculations useless. It means their limitations and factual foundation matter.
When an expert offers an opinion about what someone's alcohol concentration supposedly was at an earlier time, the defense should examine the assumptions underlying that opinion—not merely the final number.
Can You Refuse a Handheld Breath Test in Arizona?
This question requires an important distinction.
A roadside preliminary breath test should not simply be treated as interchangeable with Arizona's post-arrest chemical-testing and implied-consent procedures.
Arizona's implied-consent law can create significant consequences involving a person's driving privileges when the statutory requirements apply and a person refuses the applicable test after arrest.
That does not mean every request to blow into every device during a DUI investigation has identical legal consequences.
If you have already been arrested and are trying to determine whether you refused a test, what happened to your driver's license, or whether you need to request an MVD hearing, it is important to identify exactly which test the officer requested and what happened afterward.
Do not assume that “I refused the breathalyzer” tells the entire story.
The PBT Is Only One Part of a DUI Investigation
One of the biggest mistakes people make after a DUI arrest is focusing exclusively on the alcohol number.
The government's case may involve much more than that—and so may the defense.
When reviewing a DUI case, I may look at issues such as:
Driving evidence. Did the officer actually see the client driving? If not, how does the State establish when the driving occurred?
Body-camera footage. Does the video match the officer's written description? Does the client appear confused, impaired, nervous, tired, cooperative, or completely normal?
Field sobriety testing. Were the tests administered appropriately? Were there physical, environmental, footwear, surface, medical, or instructional issues affecting performance?
Statements. What did the client actually say about drinking? Were questions asked before or after arrest? Was the client given an opportunity to speak privately with an attorney when required?
The timeline. When was the last drink? When did driving occur? When did the stop occur? When was the PBT administered? When was the evidentiary sample obtained?
Chemical testing. Was it blood or breath? How was the sample obtained and analyzed? What documentation exists concerning the testing process?
Police conclusions. Are the officer's conclusions actually supported by what appears in the reports, video, test results, and other evidence?
Sometimes the most important part of DUI defense is identifying the difference between what an officer concluded happened and what the evidence can actually establish.
“I Blew Over .08. Do I Even Need a Lawyer?”
A breath result does not mean you should assume there is nothing to defend.
It also does not mean that every high result can simply be “thrown out.”
Good DUI defense requires something more useful than either extreme.
It requires reviewing the evidence.
An attorney can evaluate how the traffic stop began, what the officer observed, which tests were administered, what the body-camera footage shows, whether constitutional or procedural issues exist, what chemical testing was performed, and whether the State can prove each element of the charged offense.
There may be challenges to particular evidence. There may be factual defenses. There may be weaknesses useful in plea negotiations. And sometimes the evidence may be strong, in which case understanding that early can also help a client make informed decisions about how to proceed.
The number is important.
But the number is not the case.
Arrested for DUI in Tucson or Pima County?
If you were arrested for DUI after taking a handheld breath test, you do not need to figure out the significance of the result by yourself.
Amanda Bynum of AJB Law Firm, LLC represents individuals charged with DUI and other criminal offenses in Tucson and throughout Pima County. As a criminal defense attorney, former public defender, and former law professor, Amanda focuses on carefully examining the evidence and helping clients understand not only what the State is alleging, but what the evidence actually proves.
A DUI case can involve separate criminal-court and Arizona MVD issues, and some deadlines can arise quickly after an arrest.
Questions About Handheld Breath Tests?
A roadside breath test can feel like the most important piece of evidence in a DUI case. But the number on a handheld device does not tell the whole story.
Is a handheld breathalyzer the same as the breath test after a DUI arrest in Arizona?
Not necessarily. A small handheld device used during a roadside DUI investigation is often called a preliminary breath test, or PBT. That is not automatically the same as chemical testing requested after an arrest under Arizona's implied-consent laws.
If you were given more than one test—or had a breath test followed by a blood draw—it is important to determine exactly which tests were administered and when.
Can I refuse a preliminary breath test in Arizona?
A roadside preliminary breath test and a post-arrest chemical test should not automatically be treated as the same thing. Arizona's implied-consent law can impose driver's-license consequences for refusing an applicable test after arrest when the statutory requirements are satisfied.
If you have already been arrested and believe you refused testing, speak with an Arizona DUI attorney promptly because MVD deadlines may apply.
If I blew over .08 on a handheld breathalyzer, am I automatically guilty of DUI?
No. A PBT result does not automatically establish guilt. The State still has to prove the elements of the particular DUI offense charged.
A defense attorney may examine the type of device used, timing of the test, testing circumstances, evidence of driving or actual physical control, officer observations, body-camera footage, field sobriety testing, statements, and any later blood or breath test.
A number is evidence. It is not the entire DUI case.
How accurate are handheld breathalyzers?
The reliability of a particular result can depend on the device, its condition, calibration or accuracy checks, testing procedures, operator technique, timing, and the circumstances surrounding the breath sample.
Rather than assuming every handheld breathalyzer is either completely accurate or completely unreliable, a DUI defense attorney can investigate the specific device and test involved.
Can mouth alcohol affect a handheld breathalyzer result?
Residual alcohol in the mouth can potentially be relevant to breath testing because the device is intended to measure alcohol associated with the breath sample—not simply alcohol remaining in the mouth.
That is one reason the circumstances immediately before the test, including when the person last drank and what occurred before testing, may matter.
Is a roadside breathalyzer result admissible in an Arizona DUI trial?
The answer can depend on the particular evidence, the purpose for which the prosecution seeks to introduce it, and whether the required evidentiary foundation can be established.
A useful question is not simply, “Is a PBT admissible?” but “What is the State trying to prove with this result, and can it establish the foundation necessary to use it for that purpose?”
What if my roadside breath test was higher than my later blood test?
Results obtained at different times need to be evaluated in context. Alcohol concentration changes as alcohol is absorbed and eliminated from the body.
A difference between a roadside breath result and a later blood result does not necessarily mean one test must be wrong. The timeline—including when alcohol was consumed, when driving occurred, and when each sample was obtained—can be extremely important.
Can the police calculate what my BAC was when I was driving?
In some cases, the prosecution may use expert testimony and alcohol calculations to estimate a person's alcohol concentration at an earlier time. This is sometimes called retrograde extrapolation.
Those opinions rely on facts and assumptions. The defense may examine the timing of alcohol consumption, whether alcohol was still being absorbed, the elimination rate used, and other assumptions behind the calculation.
What is the Widmark formula?
The Widmark formula is a method used to estimate alcohol concentration based on variables that may include the amount of alcohol consumed, body weight, alcohol distribution, and the passage of time.
It is an estimate rather than a direct measurement of someone's BAC at the time of driving. Its usefulness depends heavily on the accuracy of the information and assumptions used.
What if the police officer never actually saw me driving?
That can be an important issue. Not every Arizona DUI investigation begins with an officer personally observing a vehicle being driven.
When police arrive after driving has ended, the evidence establishing who drove, when the driving occurred, and the person's condition at that time can become particularly significant.
Do I need a DUI lawyer if my breath or blood alcohol result was over .08?
A result over .08 does not eliminate the value of having an attorney review your case. Arizona DUI cases can involve issues involving the traffic stop, actual physical control, testing procedures, timing, constitutional rights, scientific evidence, MVD consequences, and whether the State can prove the particular charges.
Even when evidence is ultimately strong, understanding its strengths and weaknesses can help you make informed decisions about negotiation, litigation, and trial.
How soon should I contact a Tucson DUI attorney after an arrest?
It is generally better to obtain legal advice early. A DUI arrest can create issues in both criminal court and with the Arizona Motor Vehicle Division, and some MVD rights may involve relatively short deadlines.
Early representation also allows an attorney to begin identifying and preserving evidence that may be important to the defense.
Arrested for DUI in Tucson?
AJB Law Firm, LLC represents individuals facing DUI and criminal charges in Tucson and throughout Pima County. If you have questions about a handheld breath test, blood draw, chemical breath test, or alleged refusal, schedule a consultation to discuss your case.
Schedule a ConsultationIf you have questions about a DUI arrest, roadside breath test, blood test, alleged test refusal, or other DUI evidence, contact AJB Law Firm, LLC to schedule a consultation.
This article provides general educational information about Arizona DUI law and is not legal advice. Every DUI case is different, and the application of Arizona law depends on the specific facts and circumstances of the case.
