Do the police need a warrant to bring a drug-sniffing dog to your front door? The U.S. Supreme Court will soon answer that question. The case, Florida v. Jardines, may even prompt the Court to reconsider its previous Fourth Amendment dog sniff cases, United States v. Place and Illinois v. Caballes. These two decisions had held that police don't need a warrant for a dog to sniff your luggage in an airport, or your car by the side of the road, finding that the sniffs are not "searches" under the Fourth Amendment. The logic is straightforward: since a sniff "discloses only the presence or absence of narcotics, a contraband item," a search after a dog's alert cannot offend reasonable expectations of privacy. Of course, the logical flaw is equally obvious: police dogs often alert when drugs are not present, resulting in unnecessary suspicionless searches.
But do these cases track our intuitions about privacy? I recently conducted qualitative research based on the facts of Florida v. Jardines. The complete results appear in a new Stanford Law Review Online essay. I asked 187 law students whether contraband-detecting dog sniffs should be considered an invasion of privacy under a variety of false alert rates. Not surprisingly, the dogs' accuracy rates mattered significantly. Fewer than half believed that a perfectly accurate dog's sniff of a car constituted an invasion of privacy that should require a warrant or some reasonable suspicion. By comparison, two-thirds believed the sniff by the dog with a 10 percent false alert error rate needed a warrant.
But accuracy was not the only important factor; in fact, it wasn't even the most important factor. Unbeknownst to the students, the surveys randomly varied the type of contraband the dogs were trained to detect. Roughly one-third of the students responded to a hypothetical scenario involving a drug-sniffing dog, one-third responded to a bomb-sniffing dog, and one-third responded to a human cadaver-sniffing dog. Students' instincts about privacy were very sensitive to the type of criminal investigation. Those assigned to react to the drug-sniffing dog were much less tolerant of police practices. Fifty-six percent of respondents believed even the mythical perfectly accurate drug sniff constituted a Fourth Amendment search, while the corresponding rates for cadavers and bombs were 30 percent and 36 percent, respectively. The results probably reflect a shared skepticism about the efficacy and legitimacy of the "war on drugs." If the police use a dog to see if you're smoking marijuana at home, students think they should get a warrant -- but not if they're checking for dead bodies, or pipe bombs.
At present, courts do not consider the type of criminal investigation when deciding whether police conduct constitutes a search, and as a practical matter the distinction is futile. The contraband-sniffing dog is just a first-generation information-gathering tool. In time, a single instrument (possibly a drone) will detect drugs and bombs. If police conduct is sufficiently intrusive, it should not evade designation as a search simply because it is employed to achieve more worthwhile criminal enforcement goals. Conversely, unobtrusive investigatory practices should not be dismissed too quickly. Our implicit reaction to drug enforcement policies may prompt us to welcome a reversal of the previous dog sniff cases, but we may be overlooking the value of contraband-detecting technologies. Traditional suspicion-based policing is dependent on the discretion of police officers, which is prone to error and bias. Suspicionless screens, if they are used properly, redistribute the burdens of criminal investigation and punishment more equitably across the population. Our crime control policies are more likely to be carefully designed when they will apply to all of us. Police techniques that detect contraband can simultaneously improve crime detection and reduce law enforcement discretion (and, hence, potential abuse).
The Supreme Court should use the Jardines case to reconfigure Fourth Amendment analysis to accommodate both the old model of individualized suspicion and new models designed to decrease discretion. To be legitimate, these "suspicionless non-searches" should meet three criteria. The tool must have low error, be applied uniformly, and have negligible interference (that is, the tool itself should not cause adverse effects.) The dog sniff in Jardines fails all three of these elements, and there is little reason to believe dogs will ever produce a sufficiently low rate of error. But other processes and technologies have the potential to be what dogs never were -- accurate and fair. With luck, the Court will recognize a Fourth Amendment search in Jardines without creating a rule that reflexively obstructs the use of new technologies.