What Is a PBT and How Does It Work?

A Portable Breath Test (PBT) is a handheld breathalyzer device, roughly the size of a paperback book, that Arizona law enforcement officers carry on their person during traffic stops. When an officer suspects a driver may be impaired, they may ask the driver to blow into the device’s mouthpiece for approximately four seconds. The machine then analyzes the breath sample and displays an estimated blood alcohol content (BAC) reading.

The PBT is designed for use at the roadside as a quick screening tool. It is not the same device as the evidentiary breath test machine — the Intoxilyzer — used at the police station. Whether or not the officer tells you your PBT result depends on the individual officer; some always share the reading, others never do.

Are PBTs Approved for Use in Arizona DUI Investigations?

Yes. Portable breath test devices have been approved for use by the National Highway Traffic Safety Administration (NHTSA), which allows states to receive federal grant funding to purchase them.

Within Arizona specifically, PBTs have been approved for use in DUI investigations by the Arizona Department of Public Safety (DPS). However, this approval for investigative use is very different from approval as an evidentiary device — a distinction that is critically important to your DUI defense.

The Only Two Legal Uses of a PBT in Arizona

Under Arizona law, a PBT result serves exactly two functions — nothing more:

1. Establishing Probable Cause for a DUI Arrest (BAC ≥ .08%)

If a PBT result comes back at .08% or higher, an officer can use that reading as part of the basis for placing you under arrest for DUI. If you later file a motion to dismiss your case for lack of probable cause, prosecutors can introduce the PBT reading as evidence that the officer had legal grounds to arrest you. It does not prove your guilt — it only justifies the arrest itself.

2. Justifying a 20-Day Vehicle Impoundment (BAC ≥ .15%)

Arizona’s Extreme DUI law allows police to impound a driver’s vehicle for up to 20 days if a PBT result is .15% or above. This is a serious consequence that can begin at the roadside, before any more reliable testing is done. As I explain below, the inaccuracy of PBTs makes this provision particularly concerning for Arizona drivers.

Outside of these two uses, a PBT result has no legal standing in your DUI case in Arizona.

Why PBT Results Are Generally Not Admissible at Your Arizona DUI Trial

This is one of the most important facts any Arizona driver can know: PBT test results are generally not admissible as evidence of guilt at a DUI trial. Here is why.

Arizona has two ways to admit breath test results into evidence at trial:

Method 1: A.R.S. § 28-1323 (The Statutory Method)

Under Arizona Revised Statute § 28-1323, breath test results are admissible only if:

• The testing device has been approved by the Arizona DPS
• The operator holds a valid DPS permit to use that specific device
• The operator follows a DPS-approved testing checklist
• The testing sequence includes two calibration tests confirming the device is working accurately

PBT results cannot be admitted under this method because officers do not follow the required DPS procedures when administering a roadside PBT. The protocols simply are not used in the field.

Method 2: Collins v. Seidel, 142 Ariz. 587 (The Common Law Method)

Under the Arizona Supreme Court’s ruling in Collins v. Seidel and Arizona Evidence Rule 402, any relevant and scientifically reliable evidence can be admitted at trial. Breath tests can qualify under Evidence Rule 702 if an expert witness testifies that the testing method is scientifically reliable.

The problem for prosecutors is that any qualified expert in this area would testify that the DPS-approved testing protocol is the scientifically reliable method for breath testing in Arizona. Since PBT results are not obtained using those procedures, experts would conclude the results are not scientifically reliable — making them inadmissible under this method as well.

Bottom line: In the vast majority of cases, a PBT result cannot be used against you at trial to prove you were over the legal limit.

How Accurate Is a PBT? Real Arizona Case Examples

The accuracy of PBTs in Arizona varies dramatically — and that variability is one of the core reasons their results cannot be trusted as trial evidence.

In many cases I’ve handled over my 47 years as a DUI lawyer in Mesa and the greater Phoenix area, PBT readings have correlated closely with the more reliable Intoxilyzer results taken later at the station. But I’ve also seen significant discrepancies:

Case Example 1: .31% PBT vs. .16% Blood Test

One of the most dramatic variances I’ve seen personally: a PBT read .31% at the roadside. The subsequent blood test — a far more reliable method — came back at .16%. That is nearly double the actual BAC reading. A result like this can unfairly trigger a 20-day vehicle impoundment and influence how law enforcement, prosecutors, and even juries perceive your case.

Case Example 2: .173% PBT vs. .12% Intoxilyzer

More recently, I had an Arizona client whose PBT came back at .173% at the roadside. About 30 minutes later, the Intoxilyzer at the police station showed .12% — well below the .15% threshold for Extreme DUI. Despite this, my client’s vehicle was impounded for 20 days based on the inaccurate PBT result. This is a real and unjust consequence that an experienced Arizona DUI attorney must be prepared to challenge.

Why Is the PBT So Inaccurate?

• No calibration requirement: PBTs are not required to be calibrated or maintained to the same rigorous standards as the Intoxilyzer.
• Mouth alcohol issues: Officers are not required to observe a 15-20 minute deprivation period before a PBT to ensure residual mouth alcohol (from a recent drink, mouthwash, or belch) doesn’t skew the reading. This is a mandatory step for the Intoxilyzer test.
• Environmental factors: Temperature, humidity, and even radio-frequency interference can affect handheld breath testers.
• Device age and wear: Without mandatory recalibration schedules, older or heavily-used devices can drift significantly from accurate readings.

PBT vs. the Intoxilyzer at the Police Station: A Critical Difference

Arizona drivers frequently confuse the roadside PBT with the evidential breath test administered at the police station or in a testing van. This confusion can have serious legal consequences.

I’ve seen this confusion cause real problems. A driver submits to the PBT at the roadside, then gets to the station and refuses the Intoxilyzer, saying: “I already took a test — I’m not doing it again.” But under Arizona’s implied consent law, refusing the evidentiary Intoxilyzer triggers an automatic license suspension. Officers should make this distinction crystal clear, but they don’t always do so.

Do You Have to Take the PBT in Arizona?

No. The roadside portable breath test is voluntary in Arizona. You are not legally required to take it. Furthermore, if you decline the PBT, that refusal cannot be mentioned or introduced into evidence at your DUI trial. There is no penalty for declining the PBT at the roadside.

This is fundamentally different from the Intoxilyzer test at the police station. Under Arizona’s implied consent law, by operating a motor vehicle on Arizona roads you have legally agreed to submit to chemical testing (breath, blood, or urine) if lawfully arrested for DUI. Refusing the station test results in:

• A 12-month driver’s license suspension for a first refusal
• A 24-month suspension for a second or subsequent refusal

Understanding which test you are being asked to take — and whether it is mandatory — is one of the most important things you can do to protect your rights during a DUI stop anywhere in Arizona.

Frequently Asked Questions: PBTs and Arizona DUI Law

Can I refuse a portable breath test in Arizona without penalty?

Yes. The roadside PBT is voluntary. Declining does not result in any license suspension or other legal penalty, and the refusal cannot be used as evidence against you at trial. Only the evidentiary Intoxilyzer test at the police station is mandatory under Arizona’s implied consent law.

Are PBT results admissible in an Arizona DUI trial?

Generally, no. PBT results cannot be admitted under A.R.S. § 28-1323 because the DPS-required testing procedures are not followed during a roadside PBT. They also fail the scientific reliability standard required under Collins v. Seidel and Arizona Evidence Rule 702. PBT results are limited to establishing probable cause for arrest and justifying vehicle impoundment.

What happens if my PBT reading is over .15% in Arizona?

A PBT result of .15% or higher gives the officer authority to impound your vehicle for up to 20 days under Arizona’s Extreme DUI provision. This can happen even before a more accurate test is administered — and even if the more accurate test later shows a BAC below .15%. An Arizona DUI lawyer may be able to challenge an impoundment based on PBT inaccuracy.

How do I know if the PBT reading was accurate?

Comparing the PBT result to the subsequent Intoxilyzer or blood test result is the most direct measure. A significant variance between the two — especially if the PBT reading was higher — is evidence of PBT inaccuracy and can be a powerful tool in your defense. Document everything you can recall about the stop and contact a DUI attorney immediately.

Does Gordon Thompson handle DUI cases across all of Arizona?

Yes. While my office is based in Mesa, I handle DUI and criminal defense cases throughout Arizona, including Phoenix, Chandler, Gilbert, Scottsdale, Tempe, Glendale, and courts across Maricopa County and beyond. Call for a free consultation.

Charged With a DUI in Arizona? Your Next Step Matters.

A PBT reading does not determine the outcome of your DUI case. As a Mesa DUI attorney with 47 years of courtroom experience across Arizona, I know how to examine every piece of evidence — including whether a PBT reading was accurate, properly conducted, and legally used. A better outcome than you think may be possible.

Call now for your FREE consultation. I personally review every case.

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Gordon Thompson — Criminal & DUI Defense Lawyer, Mesa & Greater Phoenix, Arizona. 47 years of experience.