Can Police Search a Car for the Smell of Weed in Montana? It Gets You a DUI Check, Not the Car

The Montana Supreme Court has ruled on marijuana odor in a car twice in the last five years. Both stops happened while marijuana was still illegal, and both times the smell got the officer a DUI investigation and nothing more.

Can Police Search a Car for the Smell of Weed in Montana? It Gets You a DUI Check, Not the Car

No. The smell of marijuana in a vehicle is “sufficient particularized suspicion to expand the traffic stop into a DUI investigation at most, not a drug possession investigation” (State v. McElroy, 2024 MT 133, applying State v. Harning, 2022 MT 61). And Montana has no automobile exception: a warrantless car search needs probable cause plus a recognized exception (State v. Elison, 2000 MT 288).

Montana: odor and the car — Odor supports a DUI investigation at most. No car exception, and the dog sniff is a search. — Montana: odor and the car — the statute, the controlling cases, and what still gets you into the car. The full breakdown lives inside StreetSense, offline.

Harning (2022) — the smell buys a DUI check

Harning (Montana Supreme Court, 4–3), on a March 2018 stop: the odor of marijuana and an admission to smoking 80 miles earlier justified a DUI investigation. Once impairment was dispelled, the trooper could not hold the truck for a dog.
“After conducting the DUI investigation, Trooper DiGiovanna possessed only an undeveloped, generalized suspicion, based off the smell of marijuana, that Harning’s vehicle may have contained drugs.”

McElroy (2024) — the rule restated

McElroy (5–2), on an October 2019 stop: “Under Harning, the smell of marijuana in the vehicle would be sufficient particularized suspicion to expand the traffic stop into a DUI investigation at most, not a drug possession investigation.” The smell itself “does not constitute particularized suspicion sufficient to conclude there could be drugs in the vehicle.”
Travel, a source city, a third party’s car, nervousness and differing stories added nothing. Questions about the smell and the sniff after the driver was told “good to go” were unlawful under the Fourth Amendment and Art. II, § 11.
Both stops came before adult possession became legal on January 1, 2021. The rule was built when every ounce was illegal. We found no Montana Supreme Court odor decision on a stop made after that date.

The opening Harning left

Harning distinguished State v. Pierce, 2005 MT 182, which it described as burnt odor plus an admission that someone had smoked in the truck that day — probable cause to seize it. McElroy declined to apply Pierce because the in-car admission came only after the stop should have ended.

The dog sniff is itself a search

State v. Tackitt, 2003 MT 81 (7–0 in result): “particularized suspicion was required before the officers could use [the dog] to conduct a sniff search of the exterior of Tackitt’s vehicle.” Under Art. II, §§ 10 and 11, the sniff is a search.
Harning applied Tackitt to a traffic stop. We found no Montana decision on marijuana-trained dogs after legalization.

Elison — no automobile exception

“[T]here is no ‘automobile exception’ to the search warrant requirement under the Montana Constitution. Rather … a warrantless search of an automobile requires the existence of probable cause as well as a generally applicable exception to the warrant requirement such as a plain view search, a search incident to arrest, or exigent circumstances.”
“[T]he mobility of an automobile, without more, is not sufficient.” The Court found the search valid under the Fourth Amendment and unlawful under Art. II, §§ 10 and 11.

The statute — 16-12-106(1), MCA

Lawful acts by a person 21 or older or a registered cardholder — including “possessing, purchasing, obtaining, using, ingesting, inhaling, or transporting 1 ounce or less of usable marijuana,” with no more than 8 grams concentrated and 800 mg of THC in edibles — may not “be a basis to detain, search, or arrest.”
It protects lawful conduct. It doesn’t mention odor, states no exclusion remedy, and is subject to 16-12-108: no protection for driving under the influence, for consuming while operating, or for a passenger smoking in the enclosed compartment of a moving vehicle.

In the car, and the DUI side

61-8-1027: marijuana in the passenger area on a highway is a fine of up to $100 — not a criminal offense and not on the driving record — unless it’s in unopened dispensary packaging, a locked glove or storage compartment, the trunk or truck bed, behind the last upright seat, or a closed container in an area not normally occupied.
More than 1 ounce but less than 2 (or more than 8 but less than 16 grams concentrated): civil — forfeiture and a fine up to $200, $300 or $500, or community service (16-12-106(7)). Above that, criminal possession of dangerous drugs, 45-9-102, up to 5 years.
DUI per se: 5 ng/ml THC in blood; under 21, any THC (61-8-1002(1)(d), (e)(ii)).
For blood, get the warrant: State v. Laroque, 2026 MT 209 (not an odor case), suppressed a warrantless hospital draw, and the Court has never recognized a good-faith exception under the Montana Constitution.

The federal floor — and why it doesn't decide your case

Under the Fourth Amendment the automobile exception needs probable cause and nothing more (Maryland v. Dyson, 527 U.S. 465 (1999)), and marijuana is still illegal under federal law.
Montana’s Art. II, §§ 10 and 11 goes further twice: no automobile exception, and a dog sniff of a car is itself a search needing particularized suspicion.
That is the floor. A state court applying its own statute or constitution can — and here does — suppress what a federal court would admit. Work to your state’s rule.

How it plays out on the street

Lane-violation stop. Marijuana smell in the cab; the driver says the smoking was hours ago and miles back. That’s Harning: you can run a DUI investigation. If the field sobriety work clears the driver and you have nothing specific to the vehicle, finish the ticket and release — no dog, and no questions about the smell after “good to go” (McElroy). An open bag on the passenger seat is a 61-8-1027 citation of up to $100. If you do build probable cause of a crime, Elison still wants a warrant or a recognized exception.

Frequently asked questions

Can police search your car for the smell of weed in Montana?

No, not on the smell. In State v. Harning (2022) and State v. McElroy (2024), the Montana Supreme Court held that marijuana odor in a vehicle supports at most a DUI investigation, not a drug possession investigation. Montana also has no automobile exception, so a warrantless car search needs probable cause plus a recognized exception (State v. Elison, 2000). Both odor cases arose from stops made before adult possession became legal in 2021.

Can police bring a drug dog for the smell of weed in Montana?

Not on the smell alone. A dog sniff of a vehicle is a search under the Montana Constitution and needs particularized suspicion (State v. Tackitt, 2003). In Harning and McElroy the smell of marijuana did not supply it, and holding the vehicle for a dog was unlawful.

Is it illegal to have open weed in your car in Montana?

Under 61-8-1027, MCA, knowingly possessing marijuana in the passenger area of a vehicle on a highway is punishable by a fine of up to $100 unless it is in unopened dispensary packaging, a locked glove or storage compartment, the trunk or another area listed in the statute. It is not a criminal offense.

Carry the rule, not the guesswork. StreetSense breaks down Montana law like this — the statute, the limit, and the charge that actually sticks — verified against the code and available fully offline on shift. Start the free trial.

StreetSense is an educational reference for law enforcement, not legal advice. State law changes, and your department policy may be stricter than the statute. Always follow your state’s current rule and your agency’s policy.

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