Unreasonable search and seizure

The Fourth Amendment (Amendment IV) to the United States Constitution prohibits unreasonable searches and seizures. It requires governmental searches and seizures to be conducted only upon issuance of a warrant, judicially sanctioned by probable cause, supported by oath or affirmation, describing the place to be searched and the persons or things to be seized. It is part of the Bill of Rights and was adopted in response to the abuse of the writ of assistance, a type of general search warrant issued by the British government and a major source of tension in pre-Revolutionary America. The Fourth Amendment was introduced in Congress in 1789 by James Madison, along with the other amendments in the Bill of Rights, in response to Anti-Federalist objections to the new Constitution. Congress submitted the amendment to the states on September 28, 1789. By December 15, 1791, the necessary three-fourths of the states had ratified it. On March 1, 1792, Secretary of State Thomas Jefferson announced the adoption of the amendment.

Because the Bill of Rights did not initially apply to the states, and federal criminal investigations were less common in the first century of the nation's history, there is little significant case law for the Fourth Amendment before the 20th century. The amendment was held to apply to the states in Mapp v. Ohio (1961).

Under the Fourth Amendment, search and seizure (including arrest) should be limited in scope according to specific information supplied to the issuing court, usually by a law enforcement officer who has sworn by it. Fourth Amendment case law deals with three central questions: what government activities constitute "search" and "seizure"; what constitutes probable cause for these actions; and how violations of Fourth Amendment rights should be addressed. Early court decisions limited the amendment's scope to a law enforcement officer's physical intrusion onto private property, but with Katz v. United States (1967), the Supreme Court held that its protections, such as the warrant requirement, extend to the privacy of individuals as well as physical locations. Law enforcement officers need a warrant for most search and seizure activities, but the Court has defined a series of exceptions for consent searches, motor vehicle searches, evidence in plain view, exigent circumstances, border searches, and other situations.

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