Another problem for gauging the reliability of canines is the bias of their handlers. In a 2011 study published in Animal Cognition, the sniffing accuracy of 18 trained dogs was tested over two days. The dogs’ handlers had experience in drug and bomb detection. They were falsely told that the scents of drugs and bombs had been planted in rooms of the church where the test took place and that some of these points were marked by a piece of red paper. Recorders, who weren’t told the purpose of the study followed the dogs to write down where they raised an alert. Out of 144 searches, 123 — involving 17 of the 18 dogs — raised a false alert. Most strikingly, the handlers were most likely to claim their dogs picked up a nonexistent scent when they saw a piece of red paper.

The researchers concluded that handlers cue their dogs, deliberately or not, and this affects the animals’ accuracy. They hark back to an early-20th-century horse named Clever Hans, who appeared to be capable of counting, but whose real cleverness lay in picking up the nods and bends and smiles of his handler. When Clever Hans couldn’t see the person giving him directions, he couldn’t count. Aldo and Franky may similarly respond to signals from the officers who work with them.

Does that matter? It might if you’re the Supreme Court deciding whether a dog can sniff the front door of a house without a warrant.

In its own brief, the National Police Canine Association reports that in 2 1/2 years of service, Franky sniffed out narcotics in nearly 400 of 656, leading to the seizure of thousands of grams of cocaine, heroin, methamphetamine and marijuana. “Franky was a truly talented drug dog and served the law abiding citizens of Miami-Dade County well,” the brief says. We’re not told the dog’s rate of false positives. The canine association reassures us that when Franky didn’t alert his handler to a scent, property owners were none the wiser — their privacy wasn’t violated because they never knew their things had been sniffed.

But that, too, is questionable. Dogs cue to chemicals that are found in illegal drugs and also in all kinds of household products. Pickles and glue share an ingredient with heroin. Cocaine shares one with insecticides, perfume and food flavoring. In previous cases, the Supreme Court has ruled that the police must have a warrant to uncover intimate details at home — the temperature of the rooms in a house, for example.

Maybe we don’t want dogs to come in without a warrant and tell the police what kind of perfume someone wears either.