The use of dogs to find evidence has been taken to the Supreme Court. There appear to be two issues primarily involved, first, the reliability of dog sniffing as a means of establishing probable cause for a search:
“Dogs make mistakes. Dogs err,” lawyer Glen P. Gifford told the justices. “Dogs get excited and will alert to things like tennis balls in trunks or animals, that sort of thing.”
But Justice Department lawyer Joseph R. Palmore warned justices not to let the questioning of dog skills go too far, because they also are used to detect bombs, protect federal officials and in search and rescue operations. “I think it’s critical ... that the courts not constitutionalize dog training methodologies or hold mini-trials with expert witnesses on what makes for a successful dog training program,” he said.
“There are 32 K-9 teams in the field right now in New York and New Jersey looking for survivors of Hurricane Sandy,” Palmore added. “So, in situation after situation, the government has in a sense put its money where its mouth is, and it believes at an institutional level that these dogs are quite reliable.”
That still does not entirely get around the "Clever Hans" problem, where the dog alerts in response to subconscious clues from the handler, essentially substituting the handlers judgement for the dogs sense of smell, but testing for false positives in suspicious circumstances is a possible approach to that problem.
I also think throwing up the bomb detection and search and rescue functions is a red herring, as the evidence gathered in such cases rarely would need any probable cause for the search.
The other issue is the use of dogs to gain entry into homes where police would ordinarily be required to have a warrant to search:
In Franky’s case, Garre argued that since it wouldn’t be illegal for a police officer to sniff for marijuana outside a door, it shouldn’t be illegal for a dog like Franky to do the same thing.And a thermal imager that might be fooled by cats, cheese, tennis balls and other random objects. I gotta go with the Kagan and Ginsburg on this one.
If that’s true, said Justice Ruth Bader Ginsburg, then police could just walk down a street with drug-sniffing dogs in “a neighborhood that’s known to be a drug-dealing neighborhood, just go down the street, have the dog sniff in front of every door, or go into an apartment building? I gather that that is your position.”
“Your Honor, they could do that,” Garre said.
But if someone invented a machine called the “smell-o-matic” that could do the same thing as Franky, police would not be able to use it outside of doors without a warrant, Justice Elena Kagan said.
Police aren’t allowed to use technology to see inside a person’s closed-up home without a warrant, argued Howard K. Blumberg, the lawyer for defendant Joelis Jardines. And the use of Franky outside the house “I would submit that would basically be the same thing as a police officer walking up and down the street with a thermal imager that’s turned on,” Blumberg said.