"Canine cocaine connoisseurs” would “roam the streets at random, alerting the officers to people carrying cocaine.”

That was William Brennan in a dissent written, fittingly enough, in 1984. Tomorrow, the Supreme Court takes up the dog sniff question again, this time dealing with the home.  Adam Liptak has more:

Alan Diaz/Associated Press

The Florida Supreme Court threw out the evidence in a case involving Franky, a retired narcotics detector dog.

Aldo, a German shepherd, and Franky, a chocolate Labrador retriever, are exceptions. The Supreme Court plans to hear their cases on Wednesday.

The basic question in both cases, said Orin S. Kerr, a leading expert on the Fourth Amendment right against unreasonable search, is this: “What do you think of a dog’s nose?”

It is surely a marvel. But is it also, as the Supreme Court has suggested in previous cases, essentially infallible?

The great thing about dogs trained to sniff out drugs and other contraband, the court has said, is that they cannot invade human privacy because their noses reveal, as Justice John Paul Stevens put it in 2005, “no information other than the location of a substance that no individual has any right to possess.”

As the prosecutors in Franky’s case wrote, “anything else that the dog smells remains private.”

But there is reason to doubt that dogs are, as a brief for two groups of criminal defense lawyers put it, “binary contraband detectors.”

Justice David H. Souter, in a dissent from the 2005 decision, cited a study showing “that dogs in artificial testing situations return false positives anywhere from 12.5 to 60 percent of the time.”

“The infallible dog,” he wrote, “is a creature of legal fiction.”