Montana law requires a certified operator, an approved instrument, and regular accuracy checks before a breath result is used in a DUI case. The waiting period most people have heard about, the 15 or 20 minutes before you blow, is not in Montana's administrative rules at all. It is in the Department of Justice's operating procedure for the instrument, and the Montana Supreme Court has said the difference matters. This page is part of our Montana DUI Guide.
Where the Procedure Comes From
The Legislature told the Department of Justice to adopt uniform rules for giving tests (MCA § 61-8-1019(5)). Those rules are in the Administrative Rules of Montana, Title 23, chapter 4, subchapter 2. Alongside them, the Forensic Science Division publishes operating guides for the instrument it has approved.
| Question | Requirement | Source |
|---|---|---|
| Who may give the test | A person holding a current permit from the Forensic Science Division | MCA § 61-8-1018(1)(b)(i); ARM 23.4.218 |
| Which instrument | Only a model approved by the Division | ARM 23.4.209, 23.4.212(7) |
| Accuracy checks | Field certification at least every 31 days, laboratory certification every 365 days | ARM 23.4.213, 23.4.214 |
| Where | A location with a senior operator responsible for the instrument | ARM 23.4.215 |
| Waiting period before the test | Not in the rules. The Division's operator guide for the Intoxilyzer 9000 uses 20 minutes | Montana Senior Operator's Guide |
The Deprivation Period: 20 Minutes, by Operator Guide
A waiting period exists to let any alcohol in the mouth clear before a sample is taken, so the instrument measures breath from the lungs. Different sources call it an observation period or a deprivation period. Montana's Division uses "deprivation."
The Montana Senior Operator's Guide for the Intoxilyzer 9000 describes a "Deprivation Start Time" screen. The operator must enter when the period began, and the guide notes that this "must be at least 20 minutes prior to current time or a 'wait screen' will appear." If the 20 minutes have not been met, the instrument displays a countdown. If the instrument later reports an "Invalid Sample," the guide says that could mean mouth alcohol is present and the operator must start another deprivation period before testing again.
Two limits on that safeguard are worth understanding. The start time is typed in by the operator, so the instrument records what it was told, not what happened. And the guide separately asks the operator to confirm that the subject was observed "during sample(s) delivery," which is the blowing itself. We found no line in the guide that spells out how the subject must be watched during the 20 minutes. Our article on mouth alcohol and false readings covers why the period exists.
What the Montana Supreme Court Has Said
In State v. Levanger, 2015 MT 83, 378 Mont. 397, 344 P.3d 984, a trooper realized on the way to the detention center that he had not checked the driver's mouth. He found chewing tobacco, had the driver spit it out, and gave the Intoxilyzer 8000 test twenty minutes later. About eight of those minutes were spent driving, with the trooper watching in the rearview mirror.
The Court upheld the result. It explained that older versions of ARM 23.4.212 required compliance with the instrument's operational checklist, but the rule in effect by 2012 did not: "Today, there is no affirmative requirement in the regulations to comply with the checklist" (Levanger, ¶ 12). It then found ample evidence that the trooper had followed the suggested checklist anyway (¶ 14).
One more rule belongs in the picture. The definition of a breath "test" in ARM 23.4.201(25) says all breath analyses "must be performed in accordance with the procedures set forth by the Forensic Science Division." Levanger did not discuss that sentence. How a court would weigh it against a skipped waiting period on today's instrument is a question we cannot answer with a citation, and we will not guess.
Who May Give the Test
The rules call certified personnel "breath-test specialists" and set three levels (ARM 23.4.201(12), 23.4.216):
- Operator. Attends a Division training course, passes an examination, and demonstrates competent operation of the instrument.
- Senior operator. Holds an operator permit, completes a senior course, and demonstrates competent preparation and analysis of the standards used in field certifications.
- Technician. A senior operator, generally for at least one year, with added training in repair and maintenance.
No one may perform a breath analysis without a current permit, and permits expire on January 31 in the year following initial certification or renewal (ARM 23.4.218). A specialist who has not completed renewal before the permit expires may not perform any breath analysis until it is renewed (ARM 23.4.217(6)). The Division's guide says the Intoxilyzer 9000 will not allow testing if the operator is not current.
Field Certification of the Instrument
Under ARM 23.4.213(1), a senior operator must field certify each breath instrument at least once every 31 days using an alcohol standard approved by the Division. A field certification is a series of at least two analyses, and it is valid when the results are within plus or minus 10% of the target value. If results fall outside that range and a confirming run does not fix it, the instrument is removed from service and the Division is notified.
A field certification is also required when an instrument is first placed in service, returned to service, or used in a mobile capacity. The reports are kept at the testing location. The rule adds that failing to send a copy to the Division does not invalidate a test if the report is on file at the testing location (ARM 23.4.213(1)(h)). For the instrument itself, see the breath test machine.
What to Look For in Your Own Case
- The deprivation start time on the Breath Analysis Report Form, compared with the booking video and the patrol car video.
- Anything taken by mouth during that time, such as gum or tobacco, and any vomiting or regurgitation.
- Whether the operator's permit was current on the test date.
- The field certification before the test and the one after it, with matching serial numbers.
- Any exception message or aborted test printed before the result.
You are entitled to full information about the test on request (MCA § 61-8-1019(3)). How those records are used is covered in challenging the breath test. If a medical condition may have affected the sample, see medical conditions and breath tests.
This page explains Montana law in general as of the 2025 Montana Code Annotated and the Administrative Rules of Montana in effect on October 9, 2026. Operating procedures are set by the Forensic Science Division and may change. It is not legal advice about your specific case.