The Fourth Amendment to the United States Constitution is part of the Bill of Rights. It prohibits unreasonable searches and seizures and sets requirements for issuing warrants: warrants must be issued by a judge or magistrate, justified by probable cause, supported by oath or affirmation, and must particularly describe the place to be searched and the persons or things to be seized.
In United States criminal law, probable cause is the legal standard by which police authorities have reason to obtain a warrant for the arrest of a suspected criminal and for a court's issuing of a search warrant. One definition of the standard derives from the U.S. Supreme Court decision in the case of Beck v. Ohio (1964), that probable cause exists when “whether at [the moment of arrest] the facts and circumstances within [the] knowledge [of the police], and of which they had reasonably trustworthy information, [are] sufficient to warrant a prudent [person] in believing that [a suspect] had committed or was committing an offense.”
In criminal procedure law of the United States, an exigent circumstance allows law enforcement to enter a structure without a search warrant, or if they have a "knock and announce" warrant, allows them to enter without knocking and waiting for the owner's permission to enter. It must be a situation where people are in imminent danger, evidence faces imminent destruction, or a suspect's escape is imminent. Once entry is obtained, the plain view doctrine applies, allowing the seizure of any evidence or contraband discovered in the course of actions consequent upon the exigent circumstances.
Weeks v. United States, 232 U.S. 383 (1914) was a United States Supreme Court case in which the Court unanimously held that the warrantless seizure of items from a private residence constitutes a violation of the Fourth Amendment to the U.S. Constitution. It also prevented local officers from securing evidence by means prohibited under the federal exclusionary rule and giving it to their federal colleagues. It was not until the case of Mapp v. Ohio, 367 U.S. 643 (1961), that the exclusionary rule was deemed to apply to state courts as well.
Maryland v. Garrison, 480 U.S. 79 (1987), is a United States Supreme Court case dealing with the Fourth Amendment of the United States Constitution and the extent of discretion given to police officers acting in good faith. The Court held that where police reasonably believe their warrant was valid during a search, execution of the warrant does not violate respondent's Fourth Amendment rights.
Brigham City v. Stuart, 547 U.S. 398 (2006), is a United States Supreme Court case involving the exigent circumstances exception to the Fourth Amendment's warrant requirement. The Court ruled that police may enter a home without a warrant if they have an objectively reasonable basis for believing that an occupant is or is about to be seriously injured.
Hudson v. Michigan, 547 U.S. 586 (2006), is a United States Supreme Court case in which the Court held that a violation of the Fourth Amendment requirement that police officers knock, announce their presence, and wait a reasonable amount of time before entering a private residence does not require suppression of the evidence obtained in the ensuing search.
Payton v. New York, 445 U.S. 573 (1980), was a United States Supreme Court case concerning warrantless entry into a private home in order to make a felony arrest. The Court struck down a New York statute providing for such warrantless entries because the Fourth Amendment draws a firm line at the entrance to the house. Absent exigent circumstances, that threshold may not be reasonably crossed without a warrant. The court, however, did specify that an arrest warrant would have sufficed for entry into the suspect's residence if there had been reason to believe that the suspect was within the home.
Ker v. California, 374 U.S. 23 (1963), was a case before the United States Supreme Court, which incorporated the Fourth Amendment's protections against illegal search and seizure. The case was decided on June 10, 1963, by a vote of 5–4.
In United States criminal law, the border search exception is a doctrine that allows searches and seizures at international borders and their functional equivalent without a warrant or probable cause. Generally speaking, searches within 100 miles of the border are more permissible without a warrant than those conducted elsewhere in the U.S. The doctrine also allows federal agents to search people at border crossings without a warrant or probable cause. The government is allowed to use scanning devices and to search personal electronics. Invasive bodily searches, however, require reasonable suspicion.
Welsh v. Wisconsin, 466 U.S. 740 (1984), was a 1983 case before the US Supreme Court determining that a warrantless home arrest without exigent circumstances violates the Fourth Amendment protection against unlawful search and seizure.
United States v. Ortiz, 422 U.S. 891 (1975), was a United States Supreme Court case in which the Court held that the Fourth Amendment prevented Border Patrol officers from conducting warrantless, suspicionless searches of private vehicles removed from the border or its functional equivalent.
Wilson v. Arkansas, 514 U.S. 927 (1995), is a United States Supreme Court decision in which the Court held that the traditional, common-law-derived "knock and announce" rule for executing search warrants must be incorporated into the "reasonableness" analysis of whether the actual execution of the warrant is/was justified under the 4th Amendment. The high court thus ruled that the old "knock and announce" rule while not a hard requirement, was also not a dead letter.
Almeida-Sanchez v. United States, 413 U.S. 266 (1973), was a United States Supreme Court case holding that the search of an automobile by the United States Border Patrol without a warrant or probable cause violates the Fourth Amendment. The vehicle was stopped and searched for illegal aliens twenty-five miles (40 km) from the Mexican border. The Court approached the search from four views: automobile search, administrative inspection, heavily regulated industry inspection, and border search. As to the validity of the search under the automobile exception, the Court found no justification for the search under the Carroll doctrine because there was no probable cause. As to the validity of the search under various administrative inspection doctrines, the Court found that the officers lacked an area warrant. As to the validity of the heavily regulated industry inspection, the Court found that the doctrine is not applicable to traveling on a state highway. As to the validity of a border search, the Court found that the site of the stop and the entirety of the road on which the stop occurred was too far from the border to be considered a border search.
United States v. White, 401 U.S. 745 (1971), was a United States Supreme Court decision which held that recording conversations using concealed radio transmitters worn by informants does not violate the Fourth Amendment protection against unreasonable searches and seizures, and thus does not require a warrant.
Kentucky v. King, 563 U.S. 452 (2011), was a decision by the US Supreme Court, which held that warrantless searches conducted in police-created exigent circumstances do not violate the Fourth Amendment as long as the police did not create the exigency by violating or threatening to violate the Fourth Amendment.
Birchfield v. North Dakota, 579 U.S. 438 (2016) is a case in which the Supreme Court of the United States held that the search incident to arrest doctrine permits law enforcement to conduct warrantless breath tests but not blood tests on suspected drunk drivers.
United States v. Ramsey, 431 U.S. 606 (1977), was a United States Supreme Court case in which the Court held the search of letters or envelopes from foreign countries falls under the border exception to the Fourth Amendment to the United States Constitution, which prohibits unreasonable searches and seizures.
Mitchell v. Wisconsin, 588 U.S. ___ (2019), is a United States Supreme Court case in which the Court held that "when a driver is unconscious and cannot be given a breath test, the exigent-circumstances doctrine generally permits a blood test without a warrant."
United States v. Knights, 534 U.S. 112 (2001), was a case decided by the Supreme Court of the United States on December 10, 2001. The court held that the police search of a probationer supported by reasonable suspicion and pursuant to a probation condition satisfied the requirements under the Fourth Amendment.
