A search warrant is an order signed by a judge that authorizes police officers to search for specific objects or materials at a definite location. For example, a warrant may authorize the search of "the single-dwelling premises at 11359 Happy Glade Avenue” and direct the police to search for and seize "cash, betting slips, record books, and every other means used in connection with placing bets on horses."
Police officers obtain search warrants by convincing a neutral and detached magistrate that they have probable cause to believe that criminal activity is occurring at the place to be searched or that evidence of a crime may be found there. Usually, the police provide the judge or magistrate with information in the form of written statements under oath, called "affidavits," which report either their own observations, or those of private citizens or police informants. If the magistrate believes that the affidavit establishes probable cause to conduct a search, he or she will issue a warrant.
The suspect, who may be connected with the place to be searched, is not present when the warrant is issued and therefore cannot contest the issue of probable cause at that time. However, the suspect can later challenge the validity of the warrant.
The police can search only the place described in a warrant and for only the property that the warrant describes. They cannot search a house if the warrant specifies the backyard, nor can they search for weapons if the warrant specifies marijuana plants. However, that doesn't mean that officers can seize only those items listed in the warrant. If, in the course of their search, police officers come across contraband or evidence of a crime that is not listed in the warrant, they can often seize it.
If the warrant specifies a certain person to be searched, the police can search only that person, unless they have independent probable cause to search other persons who happen to be present at the scene. If an officer merely has a reasonable suspicion that an onlooker is engaged in criminal activity, she can only detain and question the onlooker and, if necessary for her safety, conduct a frisk for weapons (but not a full search). (For more on this topic, see below.) (Ybarra v. Illinois, 444 U.S. 85 (1979), Michigan v. Summers, 452 U.S. 692 (1981).)
Many searches occur without warrants. Over the years, courts have defined a number of situations in which a search warrant isn't necessary, either because the search is reasonable under the circumstances or because, due to a lack of a reasonable expectation of privacy, the Fourth Amendment doesn't apply at all. (For additional information to what’s below, see our section on Exceptions to the Warrant Requirement.)
What if the person in control of the premises freely and voluntarily agrees to the search? If the police limit their search to whatever the person agreed to, the search will usually be valid. But courts don’t necessarily require that the police ask for permission before searching each and every room or object; they often find that the initial consent was broad enough to justify whatever search the officers conducted, so long as the police officer’s interpretation of the consent was reasonable. For example, if a tenant consents to a search of his or her “house,” a court may determine that a reasonable interpretation of “house” includes rooms, closets, attics, and basements located within the dwelling. On the other hand, a reasonable interpretation of “house” may not include vehicles, backyard storage sheds, detached greenhouses, or any buildings or property located outside the dwelling
Courts consider consent valid if the police reasonably believed that the consenting person had the authority to consent, even if it turned out that he or she didn’t. And officers don’t have to warn people that they have a right to refuse consent to a search. (Florida v. Jimeno, 500 U.S. 248 (1991), Illinois v. Rodriguez, 497 U.S. 177 (1990), Schneckloth v. Bustamonte, 412 U.S. 218 (1973).)
Many disputes about consent have to do with who has the right to consent. If there are two or more tenants in one dwelling, courts often rule that the consent of one is enough for a search of at least some parts of the premises. (See Frazier v. Cupp, 394 U.S. 731 (1969), United States v. Matlock, 415 U.S. 164 (1973), Georgia v. Randolph, 547 U.S. 103 (2006).)
A police officer doesn’t need a warrant to seize contraband or evidence that is "in plain view" if the officer is legitimately in the area where the evidence or contraband is first spotted. (The officer must have probable cause to believe the item is evidence or contraband in order to seize it, though.) So, if an officer who has lawfully pulled you over spots what appears to be cocaine on the passenger seat, he can probably examine it, seize it, and arrest you. (Coolidge v. New Hampshire, 403 U.S. 443 (1971), Arizona v. Hicks, 480 U.S. 321 (1987).)
A police officer doesn’t need a warrant to conduct a search "incident to” an arrest. After a lawful arrest, an officer has the right to search the arrestee and the area within the arrestee’s immediate control. (United States v. Robinson, 414 U.S. 218 (1973).) (For more information, read about cellphone searches after arrest and car searches by police.)
Police may sometimes also make what's known as a "protective sweep" of the premises following an arrest. They can “sweep” if they have reason to suspect that a dangerous accomplice might be hiding in the area in question. Even without that kind of suspicion, they typically may look in spaces immediately next to the area of the arrest that could hold a hidden attacker.
A protective sweep is supposed to be limited to a cursory visual inspection of places where an accomplice might be hiding. For example, police officers can often look under beds and inside closets. If a sweep is lawful, the police can seize contraband or evidence of crime that is in plain view during the sweep. But the sweep must be aimed at protecting the officers, not gathering evidence.
As a general rule, the police are authorized to conduct a warrantless search when the time it would take to get a warrant would jeopardize public safety or lead to the loss of important evidence. Here are some situations in which most judges would uphold a warrantless search:
In these types of emergency situations, an officer's duty to protect people and preserve evidence outweighs the warrant requirement. (United States v. Santana, 427 U.S. 38 (1976), Cupp v. Murphy, 412 U.S. 291 (1973).)
A police officer may stop someone he reasonably suspects of criminal activity, and he may frisk the person for weapons if he reasonably suspects the person is armed and dangerous. This type of warrantless "search" is known as a Terry frisk. If the stop or frisk leads to probable cause for a full-blown arrest, the officer can conduct a search incident to arrest (above). (Terry v. Ohio, 392 U.S. 1 (1967); for much more on Terry stops and frisks, see our section on detentions by police.)
If you’ve been arrested or charged with a crime, or otherwise want to know how the law applies to your situation, consult an experienced criminal defense lawyer. The law can vary somewhat from state to state, and a knowledgeable lawyer can fully explain it to you.