The idea that your home is your castle lies at the heart of the Fourth Amendment's protection against unreasonable searches. So what if the police bring a dog to sniff for evidence at the castle door?
Two cases from Florida, to be argued Wednesday, ask the U.S. Supreme Court to decide when the police need a search warrant to use drug-sniffing dogs at a house, and how much legal authority a dog's alert gives police to search a car.

The front-door case comes from Dade County, where police received a Crime Stoppers tip that occupants of a house were growing marijuana. After watching the house for about 15 minutes, police and federal agents sent for Franky, a drug-sniffing dog.

But a judge threw the evidence out, ruling that "the use of a drug detector dog at the defendant's house door constituted an unreasonable and illegal search." In other words, the court said, the police should have gotten their search warrant before they sent for Franky.

The Supreme Court has upheld the authority of police, acting without a warrant, to use dogs at airports for sniffing the outside of luggage suspected of carrying contraband or to sniff the outside of cars at roadside checkpoints.