A "protective sweep" is a limited search that police are allowed to conduct when they arrest someone. The purpose of a protective sweep is to allow officers to ensure their own safety, and that of those on the scene, by searching in the vicinity of the arrest. The search is for people who may pose a threat.
Although the Fourth Amendment to the U.S. Constitution generally requires that officers have warrants before searching homes, the protective sweep doctrine is an exception. And if police discover evidence of criminal activity that is in "plain view" while conducting a protective sweep, the prosecution can typically use that evidence against the defendant at trial.
A typical protective sweep scenario involves officers having an arrest warrant for someone and needing to enter a home to make the arrest. (Protective sweeps can also involve arrests near homes (at the entrance, for example), and arrests in other kinds of buildings.) To guard against unexpected attack from unseen people in the home, the police are typically allowed to perform at least some kind of limited search of other parts of the premises.
(For information on a related topic, see Warrants and the Knock-Notice Rule.)
Courts generally recognize two levels of protective sweeps.
The first kind of prospective sweep involves officers searching closets and other spaces immediately adjoining the location where an arrest takes place—places from which an attack by some concealed person could "immediately be launched." This type of sweep doesn't require probable cause or reasonable suspicion that any danger actually exists. (Maryland v. Buie, 494 U.S. 325 (1990).)
Example: Officers Brown and Martinez have an arrest warrant for Billy. They enter his one-bedroom motel room to arrest him. The officers have no information that anyone other than Billy might be in the motel room. As a precaution, though, Officer Brown quickly looks underneath the bed and in the closet while Officer Martinez is arresting and handcuffing Billy. Brown is justified in making his search to protect Martinez and himself from a potential hiding attacker.
The second kind of protective sweep allows officers to take a broader look around the premises, but only if they have reason to believe that there's an actual danger of attack. In other words, police must be able to point to facts that would lead a "reasonably prudent" officer to believe that the area to be swept actually harbors someone posing a threat. (Maryland v. Buie, supra.)
Example: Officers Lee and Howard have an arrest warrant for Loraine for armed robbery. The local probation department has told the officers that two high-risk, violent offenders just released from jail live with Loraine in her five-bedroom home. When Officers Lee and Howard enter the home, they arrest Loraine in the living room and hear people shuffling around in the back bedrooms. Loraine tells the officers no one else is home with her. After making the arrest, Officers Lee and Howard go into the back bedrooms, where they find drugs and one of the roommates with a gun. The officers were justified in "sweeping" the back bedrooms, and the drug and gun evidence will be admissible in court.
Because protective sweep searches are for the safety of officers and others—not the gathering of evidence—they must be limited, in time and scope. A lawful protective sweep isn't a full search, but rather a "cursory inspection" of the places where a person could be hiding. (Maryland v. Buie, supra.)
Place. During a protective sweep, officers may look only in areas where a person could be hiding.
Time. Protective sweeps generally must be quick. The search can last only as long as it takes to dispel the risk of danger, and no longer than it takes to arrest the subject and leave the premises.
In deciding whether a protective sweep was reasonable, courts tend to look at the "totality of the circumstances"—in other words, all the relevant factors. The following are some of the factors courts have considered:
Most state and federal courts have extended the protective sweep rule beyond cases involving arrest. A number of courts have applied the rule to cases where someone consents to the police entering a portion of a home, and officers find it necessary to sweep other parts of the home for purposes of safety. Courts have also applied the protective sweep rule to probation searches and searches conducted pursuant to search warrants. The minority of state and federal courts have interpreted the rule as only applying when an arrest is actually made by officers.
The legality of a protective sweep depends heavily on the facts. And courts differ somewhat in their approach to the issue. As the section above shows, protective sweep law may vary at least slightly between states. You should always rely for legal advice on an attorney with experience in your locale.