The Fourth Amendment
The Fourth Amendment protects the people against unreasonable searches and seizures by the government. It requires warrants to be supported by probable cause and to describe with particularity the place to be searched and the items to be seized.
Ratified in 1791, the Fourth Amendment reads: "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." Its target was the general warrant, a writ of assistance the British Crown had used to authorize sweeping searches of colonial homes and warehouses without specific suspicion. James Otis denounced the writs in a 1761 Boston argument that John Adams later called the moment the child of independence was born.
The amendment binds federal officers from the founding and, after Wolf v. Colorado in 1949 and Mapp v. Ohio in 1961, binds state and local officers as well. The Supreme Court has developed a vast body of doctrine to give the words operational meaning. A search generally requires a warrant supported by probable cause, with carefully drawn exceptions for exigent circumstances, consent, vehicles, plain view, searches incident to lawful arrest, and a few others. Evidence obtained in violation of the amendment is generally excluded from criminal trials under the exclusionary rule established in Weeks v. United States in 1914.
The rise of the digital age has reshaped Fourth Amendment doctrine. The Court held in Katz v. United States in 1967 that the amendment protects reasonable expectations of privacy, not merely physical spaces. It applied that framework to government tracking in United States v. Jones in 2012, to cell phone searches in Riley v. California in 2014, and to historical cell-site location data in Carpenter v. United States in 2018. The amendment's text has not changed in more than two centuries. The technologies it must restrain have changed in ways the founders could not have imagined. The interpretive challenge of the next generation will be to apply the principles of 1791 to surveillance tools that did not exist a decade ago.