WASHINGTON -- The Supreme Court ruled Tuesday that police cannot bring drug-sniffing police dogs onto a suspect's property to look for evidence without first getting a warrant for a search, a decision which may limit how investigators use dogs' sensitive noses to search out drugs, explosives and other items hidden from human sight, sound and smell.

The high court split 5-4 on the decision to uphold the Florida Supreme Court's ruling throwing out evidence seized in the search of Joelis Jardines' Miami-area house. That search was based on an alert by Franky the drug dog from outside the closed front door.

Justice Antonin Scalia said a person has the Fourth Amendment right to be free from the government's gaze inside their home and in the area surrounding it, which is called the curtilage.

"The police cannot, without a warrant based on probable cause, hang around on the lawn or in the side garden, trawling for evidence and perhaps peering into the windows of the home," Justice Antonin Scalia said for the majority. "And the officers here had all four of their feet and all four of their companion's, planted firmly on that curtilage - the front porch is the classic example of an area intimately associated with the life of the home."

He was joined in his opinion by Justices Clarence Thomas, Ruth Bader Ginsburg, Sonia Sotomayor and Elena Kagan.

The four justices who dissented were Chief Justice John Roberts, Justice Stephen Breyer, Justice Anthony Kennedy and Justice Samuel Alito.

It's not trespassing when a mail carrier comes on a porch for a brief period, Alito said. And that includes "police officers who wish to gather evidence against an occupant," Alito said. "According to the court, however, the police officer in this case, Detective Bartelt, committed a trespass because he was accompanied during his otherwise lawful visit to the front door of the respondent's house by his dog, Franky. Where is the authority evidencing such a rule?"

Alito also said that the court's ruling stretches expectations of privacy too far. "A reasonable person understands that odors emanating from a house may be detected from locations that are open to the public, and a reasonable person will not count on the strength of those odors remaining within the range that, while detectable by a dog, cannot be smelled by a human."

It was not the dog that was the problem, Scalia said, "but the behavior that here involved use of the dog."

"We think a typical person would find it 'a cause for great alarm' to find a stranger snooping about his front porch with or without a dog," Scalia said. "The dissent would let the police do whatever they want by way of gathering evidence so long as they stay on the base path, to use a baseball analogy - so long as they 'stick to the path that is typically used to approach a front door, such as a paved walkway.' From that vantage point they can presumably peer into the house with binoculars with impunity. That is not the law, as even the state concedes."

Thousands of dogs are used by governmental organizations around the United States to track criminals, sniff out illegal items like explosives at airports and search wreckage sites like bombed buildings and hurricane or earthquake-destroyed homes for injured people.

On the morning of Dec. 5, 2006, Miami-Dade police detectives and U.S. Drug Enforcement Administration agents set up surveillance outside a house south of the city after getting an anonymous tip that it might contain a marijuana growing operation. Detective Douglas Bartelt arrived with Franky and the two went up to the house, where Franky quickly detected the odor of pot at the base of the front door and sat down as he was trained to do.

That sniff was used to get a search warrant from a judge. The house was searched and its lone occupant, Jardines, was arrested trying to escape out the back door. Officers pulled 179 live marijuana plants from the house, with an estimated street value of more than $700,000.

Jardines was charged with marijuana trafficking and grand theft for stealing electricity needed to run the highly sophisticated operation. He pleaded not guilty and his attorney challenged the search, claiming Franky's sniff outside the front door was an unconstitutional law enforcement intrusion into the home.

The trial judge agreed and threw out the evidence seized in the search, but that was reversed by an intermediate appeals court. In April a divided Florida Supreme Court sided with the original judge.

That ruling was upheld by the Supreme Court's decision, the latest in a long line of disputes about whether the use of dogs to find drugs, explosives and other illegal or dangerous substances violates the Fourth Amendment protection against illegal search and seizure. The court has OK'd drug dog sniffs in several other major cases. Two of those involved dogs that detected drugs during routine traffic stops. In another, a dog hit on drugs in airport luggage. A fourth involved a drug-laden package in transit.

The difference in this case, the court said, is that Franky was used at a home.

"A drug detection dog is a specialized device for discovering objects not in plain view (or plain smell)," Kagan wrote in a concurring opinion. "That device here was aimed at a home - the most private and inviolate (or so we expect) of all the places and things the Fourth Amendment protects. Was this activity a trespass? Yes, as the court holds today. Was it also an invasion of privacy? Yes, that as well."

This is the second decision this year on the use of drug-sniffing dogs by police. The court unanimously ruled earlier in another Florida case that police don't have to extensively document the work of drug-sniffing dogs in the field to be able to use the results of their work in court.

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The case was Florida v. Jardines, 11-564.

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