An Appeals Court in California rejected (for now) an argument brought by the prosecution that an officer who smells unlit marijuana in a closed bag does not need a search warrant. But the Court also suggested that California's highest court needs to revisit this issue. See: http://www.law.com/jsp/ca/PubArticleCA.jsp?id=1202520041375
Ohio's Supreme Court has already held in 2001 that the odor or marijuana (lit or unlit) may form the basis for a warrantless search. The Ohio Supreme Court stated:
Many state and federal courts have previously confronted this issue and concluded that the detection of the odor of marijuana, alone, by an experienced law enforcement officer is sufficient to establish probable cause to conduct a reasonable search. See, e.g., People v. Kazmierczak (2000), 461 Mich. 411, 413, 605 N.W.2d 667, 668 ("the smell of marijuana alone by a person qualified to know the odor may establish probable cause to search a motor vehicle"); [*50] Mendez v. People (Colo.1999), 986 P.2d 275, 280 ("the smell of burning marijuana may give an officer probable cause to search or arrest"); State v. Secrist (1999), 224 Wis. 2d 201, 210, 589 N.W.2d 387, 391 ("The unmistakable odor of marijuana coming from an automobile provides probable cause for an officer to believe that the automobile contains evidence of a crime."); Green v. State (1998), 334 Ark. 484, 490, 978 S.W.2d 300, 303 ("the odor of marijuana emanating from a particular bag located on a bus is sufficient to provide probable cause to conduct a search of that bag"). Likewise, federal courts share this view.
The Court then went on to state:
"[I]f the smell of marijuana, as detected by a person who is qualified to recognize the odor, is the sole circumstance, this is sufficient to establish probable cause. There need be no additional factors to corroborate the suspicion of the presence of marijuana."
Obviously, pot smokers have to drive much more carefully in Ohio.