 They're looking for the odor of alcohol, odor of marijuana. If it's not there, if they don't see the signs of intoxication, they move on. But the last one is the kicker. The last one is the one that really pulls it out of the purview of Fourth Amendment, and it's that. DUI roadblocks must be publicly advertised in advance through local newspapers, news reports, and police department websites to give the public an opportunity to say, I don't want to drive that way.