The US high court ruled that bringing a drug sniffing dog into a private home is a "search" within the meaning of the Fourth Amendment of the Constitution and is not allowed without a warrant.
The 5-4 vote upheld a 2011 Florida Supreme Court ruling that dismissed evidence found after police brought a drug sniffing dog near a home and alerted officers to the presence of marijuana.
The case was thrown out after the court said the police officers involved did not have probable cause to "search" the home with the police dog.
The ruling will likely have implication for when and how police can use trained dogs to detect illegal drugs without first getting a warrant.
"A police officer not armed with a warrant may approach a home and knock, precisely because that is no more than any private citizen might do," Justice Antonin Scalia wrote for the majority.
"But introducing a trained police dog to explore the area around the home in hopes of discovering incriminating evidence is something else," he added. "There is no customary invitation to do that."
In a dissenting opinion, Justice Samuel Alito noted that a police officer was able to smell marijuana upon approaching the house.
"The conduct of the police officer in this case did not constitute a trespass and did not violate respondent's reasonable expectations of privacy," Alito wrote.
"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."
The ruling is the second of two sniffer dog cases considered by the Supreme Court this term.
On Feb. 19 the high court upheld the use of drug sniffing dogs during routine traffic stops, allowing police to search the vehicle after a police dog has detected the presence of drugs.