A breath test result in a Montana DUI case is challenged by checking four things: who gave the test, whether the instrument was properly certified, what happened in the minutes before the sample, and what the number does and does not prove about the time you were driving. Each has a statute, an administrative rule, or a Montana Supreme Court decision behind it. This page expands the breath test section of our Montana DUI defenses page and is part of our Montana DUI Guide.
The Rules and the Foundation Checklist
Breath testing in Montana is governed by MCA §§ 61-8-1018 and 61-8-1019 and by the Department of Justice's rules at ARM Title 23, chapter 4. The Montana Supreme Court has explained why compliance matters. DUI is an absolute liability offense, the test result is often the critical proof, and so "a defendant charged with driving under the influence deserves the procedural safeguards contained in the administrative rules to ensure the accuracy of such highly relevant evidence" (State v. Frickey, 2006 MT 122, ¶ 18, 332 Mont. 255).
| Question | The rule | Source |
|---|---|---|
| Was the operator certified? | A breath test report is admissible if the test was performed by a person certified by the Forensic Science Division to administer it. | MCA § 61-8-1018(1)(b)(i) |
| Was the instrument model approved? | All models used for testing must be approved by the division. | ARM 23.4.209 |
| Was the instrument within field certification? | Field certified for accuracy at least once every 31 days by a senior operator. A certification is valid for 31 days forward. | ARM 23.4.213(1), (1)(j) |
| Was the certification itself valid? | At least two analyses with an approved alcohol standard, with results within plus or minus 10% of the target value. | ARM 23.4.213(1)(a), (b) |
| Was the standard solution in date? | A water standard may not be used for longer than three months after first use. A gas standard may not be used past its expiration date. | ARM 23.4.213(1)(c) |
| Were the records on file? | Field certification results must be on file at the testing location before the instrument is used for subject testing. | ARM 23.4.213(1)(e) |
If results from a field certification fall outside the range and are still out on confirmation, the instrument must be removed from service (ARM 23.4.213(1)(d)). A defense review asks for the field certification reports on both sides of your test date, not only the one before it.
What the Supreme Court Has Done With These Rules
In State v. Incashola, 1998 MT 184, 289 Mont. 399, the Court held that the rule making a field certification valid for a set number of days forward is a foundation requirement: a proper certification within that period is an adequate foundation, and its absence makes the result inadmissible (¶ 16). The period was 7 days when Incashola was decided. The current rule says 31. The State won that appeal, because the certification in that case was timely.
In State v. Frickey, the instrument had gone more than thirteen months without the annual laboratory certification the rules then required. The Court held that the trial court should have suppressed the result (¶ 20). The rules have been amended several times since 2006, so the lesson is the principle, not the particular interval: the State must show the certification that the rules in effect on your test date required.
The other half of the picture is in ARM 23.4.213(1)(i). A field certification before a test, together with calibration checks during the test or a field certification afterward, creates an inference that the instrument was in proper working order. Both sides may offer other evidence on that point.
The Minutes Before the Sample
Breath instruments are meant to measure deep lung air (ARM 23.4.212(7)). The concern in the minutes before a test is anything that could put alcohol in the mouth. In State v. Flaherty, 2005 MT 122, 327 Mont. 168, the defendant argued the test was invalid because he had not been closely observed for 15 minutes to be sure he put nothing in his mouth and did not belch or regurgitate. The Court looked at the operational checklist actually in use and found it required that no oral ingestion of any material occur during the 15 minutes before testing and that the person be observed during sample delivery. It did not require the administrator to keep eyes on the person at all times (¶ 15), and the result came in.
The practical point is to get the checklist that was used in your case and the station video, and compare them. The text of the rules we read for this page does not itself state an observation period, so the checklist is where to look. Our pages on mouth alcohol and false readings and medical conditions and breath tests cover the physiology.
Timing and a Rising Alcohol Level
A breath test happens after the driving, sometimes well after. People reasonably ask whether their level was lower on the road than at the station. In State v. McGowan, 2006 MT 163, 332 Mont. 490, the defendant tested 0.092 about 50 minutes after the stop and argued exactly that. The Court held that breath tests given within a reasonable time after the alleged act are consistent with the per se statute, and that the State need not present retrograde extrapolation evidence relating the number back to the time of driving (¶¶ 17 to 21).
So a rising level is not a defense the law hands you. It is an argument about weight that needs facts: when you last drank, what you ate, and when the test was taken. For an impairment charge, the statute makes the inference from a result of 0.08 or more rebuttable (MCA § 61-8-1002(2)(c)). See rising BAC.
The Roadside Screening Test Is Different
The handheld preliminary alcohol screening test may be requested only if both the officer and the instrument are certified (MCA § 61-8-1016(1)(c)), and under ARM 23.4.225 its results are recorded only as positive or negative. In State v. Gieser, 2011 MT 2, 359 Mont. 95, a deputy used a handheld unit that was out of certification, the number was put before the jury without objection, and the Court reversed the conviction because defense counsel's failure to object, to that and to unsupported eye-test testimony, was ineffective assistance.
Getting the Records
- the breath analysis report form and the operational checklist for your test;
- the operator's certification;
- the instrument's field certification reports around your test date, with the lot number and dates for the alcohol standard;
- maintenance or out-of-service records for that instrument;
- video from the testing room.
Field certification reports are kept at the testing location and copies go to the division (ARM 23.4.213(1)(g)). Full information about any test given at an officer's direction must be made available on request (MCA § 61-8-1019(3)), and the prosecutor must disclose the results of scientific tests (MCA § 46-15-322(1)(c)).
Honest Limits
Often the operator was certified and the instrument was within its 31 days, and the records show it. The Court has also allowed certification records to be considered for foundation purposes without live testimony from their custodian (State v. Delaney, 1999 MT 317; State v. Jenkins, 2011 MT 287). A breath test challenge is worth making when the records show a gap, not as a matter of routine. And an impairment charge under MCA § 61-8-1002(1)(a) can proceed on other evidence even if the number is excluded. If the stop itself is in question, see challenging the traffic stop.
This page explains Montana law in general as of the 2025 Montana Code Annotated, the Administrative Rules of Montana in effect on October 9, 2026, and the decisions cited. Every case turns on its own facts, and past results do not predict future outcomes. It is not legal advice about your specific case.