The Fourth Amendment to the U.S. Constitution protects individuals from unreasonable searches and seizures and requires that the issuance of a warrant be supported by probable cause.
The U.S. Supreme Court recently ruled that a police drug-sniffing dog could not be used without a warrant to search near a suspected drug dealer's home. In Florida v. Jardines, the Supreme Court upheld a suppression ruling in a marijuana case where the police used a drug sniffing dog outside the home of a suspected drug dealer and then got a warrant to search the home based upon the alerts of the dog.
In a 5-4 ruling, the Court found that using a dog to investigate a home and its surroundings required a warrant, as it was a "search" within the meaning of the 4th Amendment. As Justice Scalia indicated, the Fourth Amendment extends no both a house and its surroundings.
The Court reasoned that there is an implicit license for visitors (whether police or private citizens) to approach the front door of a house and knock, and then wait to be greeted and promptly leave. However, the Court reasoned that there was no implicit license for a trained police dog to explore around the home to look for incriminating evidence.
One of the important things to note from this decision is that it pertains to using drug-sniffing dogs to investigate the immediate surroundings of a home. Different rules apply to the use of drug-sniffing dogs in relation to vehicle stops or at the airport.
This Jardines decision reinforces the rights of homeowners to be free from unreasonable searches and seizures in not only their home, but also the area surrounding their home.