For all their use by law enforcement across the country, drug‐​sniffing dogs haven’t gotten a lot of consideration in the Supreme Court. In a pair of cases next fall, though, the Court seems likely to give them some attention. Florida v. Harris is one of the cases it has taken. Harris will examine “[w]hether an alert by a well‐​trained narcotics detection dog certified to detect illegal contraband is insufficient to establish probable cause for the search of a vehicle.”

This week, we filed an amicus brief in the other drug‐​sniffing dog case, coming out of the same state. Florida v. Jardines asks whether the Fourth Amendment would be implicated if the government brought a drug‐​sniffing dog to the front door of your home seeking the scent of illegality.

What the Court has done with drug‐​sniffing dogs so far is not very good. We homed in on the major precedent, Caballes, to illustrate the weakness of the “reasonable expectation of privacy” test that originated in United States v. Katz (1967).

In Illinois v. Caballes, 543 U.S. 405 (2005), this Court did not apply Katz analysis. It did not examine (or even assume) whether Roy Caballes had exhibited a subjective expectation of privacy, the first step in the Katz test. Thus, the Court could not take the second step, examining its objective reasonableness.

Instead, the Caballes Court skipped forward to a corollary of the Katz test that the Court had drawn in United States v. Jacobsen, 466 U.S. 109 (1984): “Official conduct that does not ‘compromise any legitimate interest in privacy’ is not a search subject to the Fourth Amendment.” Caballes, 543 U.S. at 408 (quoting Jacobsen, 466 U.S. at 123).

This is a logical extension of the Katz test, and one that helps reveal its weakness in maintaining the Fourth Amendment’s protections consistently over time. Now, instead of examining whether searches and seizures are reasonable, courts applying the Jacobsen/Caballes corollary can uphold any activity of government agents sufficiently tailored to discovering only crime.

What kinds of activities might those include? We talked about lasers.

A DHS program that might be directed not only at persons, but also at their houses and effects, is called the “Remote Vapor Inspection System” (or RVIS). RVIS “generates laser beams at various frequencies” to be aimed at a “target vapor.” Beams “reflected and scattered back to the sensor head” reveal “spectral ‘signatures’” that can be compared with the signatures of sought‐​after gasses and particulates. [citations omitted] Using RVIS, government agents might remotely examine the molecular content of the air in houses and cars, quietly and routinely explore the gasses exiting houses through chimneys and air ducts, and perhaps even silently inspect any person’s exhaled breath. If RVIS technology is programmed to indicate only on substances that indicate wrongdoing, the Jacobsen/Caballes corollary extinguishes the idea that its pervasive, frequent, and secret use would be a search.

If a dog sniff only reveals illegal activity, compromising no privacy interest, it’s not a search. So using lasers to check your breath for illegal substances is not a search either. We hope, obviously, that the Court will do away with this rule, which is so attenuated from both the language and the purpose of the Fourth Amendment.

Instead of determining whether a person has “reasonable expectations of privacy”—we called that doctrine a “jumble of puzzles”—courts should examine whether a “search” has occurred by seeing if police accessed something that was hidden from view.

When a person has used physics and law to conceal something from others, the Fourth Amendment and the Court should back those privacy‐​protective arrangements, breaching them only when there is probable cause and a warrant (or some exception to the warrant requirement).

To hold otherwise would be to allow the government to invade privacy not just using drug‐​sniffing dogs but using ever more sophisticated technology.