Under the Fourth Amendment of the U.S. Constitution, individuals are protected from unreasonable searches and seizures that are not accompanied by a warrant or supported by probable cause.
There are a small number of exceptions to the warrant requirement when police can conduct a search and seizure. A 2011 Supreme Court case, Kentucky v. King, explained the limits of the exigent circumstances exception to the warrant requirement when officers search a private residence.
In Kentucky v. King, police officers followed a suspected drug dealer to an apartment complex where they smelled marijuana coming from one of the apartment doors. Officers knocked on the door and announced their presence. Officers at the scene testified that when they began knocking they could hear movement within the apartment that sounded like the occupants were destroying evidence. Law enforcement officers kicked the door in and found marijuana and cocaine in plain view during a protective sweep of the apartment.