The US Supreme Court ruled Tuesday that police overstepped their authority by sending a sniffer dog to a man's front door to search for marijuana, saying authorities needed a search warrant.
The top court agreed with a Florida man, Joelis Jardines, who objected after police sent a trained dog named Franky to his door in 2006. After the dog detected the smell of marijuana, police obtained a warrant to search the home.
The Supreme Court ruled that the door area formed part of Jardines' home and thus was protected under the US Constitution's Fourth Amendment, which protects citizens against "unreasonable searches" by the government.
Writing for the majority, Justice Antonin Scalia dismissed the argument that the police were acting no differently than cookie-selling Girl Scouts or Halloween trick-or-treaters who routinely approach strangers' doors.
"To find a visitor knocking on the door is routine (even if sometimes unwelcome)," Scalia wrote.
"To spot that same visitor exploring the front path with a metal detector, or marching his bloodhound into the garden before saying hello and asking permission, would inspire most of us to -- well, call the police," he wrote.
Scalia, writing for five of the nine justices, upheld a decision of the Florida Supreme Court that said that evidence from the dog could not be used against Jardines as the "search" had not been supported by probable cause.
The opinion of Scalia, known as a conservative, was supported by three justices seen as belonging to the court's liberal wing.
The liberal trio, in a concurring opinion authored by Justice Elena Kagan, argued that police violated Jardines' right to a reasonable expectation of privacy.
In a dissent, Justice Samuel Alito said that the sniffer dog did not constitute a search under the Fourth Amendment. He pointed to the long use of dogs in law enforcement, citing a 1318 law in Scotland.
"If bringing a tracking dog to the front door of a home constituted a trespass, one would expect at least one case to have arisen during the past 800 years. But the court has found none," Alito wrote.
The Supreme Court did not forbid the use of sniffer dogs in general. In a ruling last month on a separate case in Florida, the court unanimously rejected objections to the dog.
In that case, the Supreme Court ruled that police had probable cause to search a car after a tip from a sniffer dog during a traffic stop, despite complaints over the animal's reliability.