Can Police Conduct a Search Without a Warrant?
In most cases, police need a warrant to conduct a search. Police get a warrant by showing a judge or magistrate that there is sufficient probable cause to conduct a search. If the judge determines that there is sufficient probable cause, then a warrant will be issued for police to search for specific items in a specific place. Often the description of what's being sought might be somewhat general, like "drug paraphernalia and anything associated with the buying, selling or using of illegal substances."
There are three common exceptions to the rule that police need to obtain a warrant before conducting a search. The first, called the "plain view doctrine," refers to situations in which the police, during the course of legal police business, see something of interest in plain view. For example, if you have consented to talk to the police inside your home, and an officer happens to see drug paraphernalia or an item fitting the description of a something that has recently been stolen, an officer can legally seize the evidence without a warrant.
Second, the police can also legally conduct a warrantless search if you give consent for them to do so. Finally, a police officer can conduct a "search incident to arrest" without a warrant. This means that during the course of a lawful arrest - one that's based on probable cause - the police can search the arrestee and the immediate surroundings for weapons or for evidence the police fear might be destroyed. The search is limited, however, to the area within the suspect's "immediate control." This usually means that police cannot search beyond the room they are in when they make the arrest. If police believe there might be other armed suspects in the building, they can do what's called a "protective sweep" to look for people who might be hiding. In the course of a protective sweep, police can then legally seize anything incriminating within plain view.
There are also emergency situations, known as "exigent circumstances," in which a police officer can search without a warrant. For example, an officer can follow a fleeing suspect into his house and search for evidence the officer believes the suspect intends to destroy. The same holds true if an officer has reason to believe that someone is in danger. If he hears cries coming from inside a house, an officer can enter, make an arrest and perform a search incident to arrest.