What is a “Search” and Why Doesn a Dog Sniff Qualify?
Why not? To begin, under longstanding Supreme Court precedent, not all police investigative measures constitute “searches” implicating the Fourth Amendment. To give an obvious example, if a cop on the beat observes an assault, clearly the mere act of viewing what is plain for everyone to see is not a “search.” Or, to give an example closer to the facts of Caballes, if a police officer patrolling a public park smells marijuana coming from a group of teenagers smoking on a bench, that ordinary use of his olfactory senses is not a “search” either. Under the relevant precedents, police activity only constitutes a Fourth Amendment “search” if it violates a “reasonable expectation of privacy.” In our two hypothetical examples, it is not reasonable to expect privacy in activity conducted in public, where it can be seen or smelled by any passersby, including the police. Of course, the state trooper who shepherded the police dog around Caballes’s car was not a mere passerby. He specifically tar
