The handheld breath device used at the roadside in Montana is a preliminary alcohol screening test, or PAST (many people call it a PBT). It is a screening tool used to estimate alcohol concentration before an arrest. It is covered by the implied consent law, so refusing it has license consequences, but taking it does not replace the evidentiary test that follows an arrest. This page is part of our Montana DUI Guide.
What the Statute Says About the PAST
Four sentences in MCA § 61-8-1016(1) define the test:
- A person who drives or is in actual physical control of a vehicle on the ways of this state open to the public is considered to have consented to tests of blood, breath, or oral fluid.
- Those tests include "a preliminary alcohol screening test of the person's breath for the purpose of estimating the person's alcohol concentration."
- A PAST may not be conducted or requested unless both the peace officer and the instrument have been certified by the department under its rules.
- The obligation to submit to a test "is not satisfied by the person submitting to a preliminary alcohol screening test."
When an Officer Can Ask for One
The statute does not allow a PAST at every stop. Before an arrest, a test must be administered at an officer's direction when the officer has particularized suspicion that the person has been driving or in actual physical control while under the influence, and the person has been detained for DUI (MCA § 61-8-1016(2)(a)(i)). For a driver under 21, the trigger is particularized suspicion of a violation of the under-21 limits (MCA § 61-8-1016(2)(a)(ii)).
That is the same level of suspicion Montana requires before field sobriety tests. A stop for a taillight, with nothing pointing to alcohol, does not supply it.
PAST Versus the Test After Arrest
| Question | Roadside PAST | Evidentiary breath or blood test |
|---|---|---|
| Where and when | At the roadside, usually before an arrest. | At a station or detention center, after an arrest or one of the other statutory triggers. |
| Purpose in the statute | "Estimating the person's alcohol concentration" (MCA § 61-8-1016(1)(b)). | Determining any measured amount or detected presence of alcohol (MCA § 61-8-1016(1)(a)). |
| What the officer needs | Particularized suspicion of DUI and a detention for it, with a certified officer and a certified instrument. | The grounds listed in MCA § 61-8-1016(2)(a), most often probable cause and an arrest. |
| Does taking it end the matter? | No. It does not satisfy the obligation to take the later test. | Yes, as to that test. The officer designates which test or tests are given. |
| How results are recorded under the rules | Positive or negative only, with 0.020 or more counted as positive (ARM 23.4.225). | A reported alcohol concentration from an approved, field-certified instrument. |
The instrument used after arrest is covered in the breath test machine.
Refusing the Roadside Test
The officer must inform you of the right to refuse the test and that refusal will result in suspension of your license for up to 1 year (MCA § 61-8-1016(2)(c)). Because the PAST is one of the implied consent tests, a refusal can be reported to the Motor Vehicle Division, which suspends the license for the period in MCA § 61-8-1032: 6 months for a first refusal, or 1 year for a second or later refusal within 5 years of a previous one, with no probationary license.
Two details soften that slightly. Refusing the PAST and then another test in the same incident is a single refusal for suspension purposes (MCA §§ 61-8-1016(2)(e), 61-8-1032(2)(e)). And a suspension can be challenged by petition within 30 days, where the court looks at whether the officer had a basis to request the test and whether there was a refusal (MCA § 61-8-1017). See challenging a refusal suspension and our test refusal page.
Is the Number Admissible at Trial?
This question has a long history, and the short version is: not automatically.
- The older rule. In State v. Strizich, 286 Mont. 1 (1997), as the Court later described it, PAST results were treated as an estimate for establishing probable cause to arrest, not as substantive evidence of the amount of alcohol in a person's body.
- The statute changed. The Legislature amended the evidence statute to list the PAST among admissible tests. Today's version makes a report admissible if a preliminary alcohol screening test was performed by a person certified by the Forensic Science Division (MCA § 61-8-1018(1)(b)(i)).
- The Court still asked for proof. In State v. Weldele, 2003 MT 117, and State v. Crawford, 2003 MT 118, the Court held it was error to admit the PAST number because the State had not shown the field result was reliable. In Crawford, where the driver had refused the station test and the PAST was the only number before the jury, the Court did not treat the error as harmless.
- Then the State met its burden. In State v. Damon, 2005 MT 218, the State presented testimony about the device's accuracy, the Court affirmed admission of a result of 0.274, and it said concerns about field conditions go to the weight of the evidence and can be raised on cross-examination. The Court left open whether the administrative rules for the device are adequate.
So a prosecutor who wants the jury to hear the roadside number should expect to lay a foundation, and a defense lawyer should expect to test it: the certification of the officer and the device, how the test was given, and the conditions at the roadside. The administrative rule adds another wrinkle. It says PAST results are to be reported only as positive or negative (ARM 23.4.225).
How the PAST Is Used Before Trial
Even when the number never reaches a jury, the PAST does real work earlier in the case. A positive result is commonly part of the officer's probable cause for arrest, and it may be cited at a suppression hearing or a license hearing. In Damon, the defense expert pointed to limits of the handheld device, including that it cannot detect mouth alcohol. That subject is covered in mouth alcohol and false readings.
What a Defense Lawyer Looks At
- Did the officer have particularized suspicion of DUI before asking for the test?
- Were the officer and the instrument certified, as the statute requires?
- Was the advisory about the right to refuse and the suspension given?
- If there was a refusal, was it reported correctly, and was a petition filed within 30 days?
- If the State wants to use the number, can it prove the result is reliable?
This page explains Montana law in general as of the 2025 Montana Code Annotated, the Administrative Rules of Montana, and the court decisions cited. It is not legal advice about your specific case.