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 standard by which police authorities have reason to obtain a warrant for the arrest of a suspected criminal or the issuing of a search warrant. There is no universally accepted definition or formulation for probable cause. One traditional definition, which comes from the U.S. Supreme Court's 1964 decision Beck v. Ohio, is when "whether at [the moment of arrest] the facts and circumstances within [an officer's] knowledge 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."
Search and seizure is a procedure used in many civil law and common law legal systems by which police or other authorities and their agents, who, suspecting that a crime has been committed, commence a search of a person's property and confiscate any relevant evidence found in connection to the crime.
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.
Knock-and-announce, in United States law criminal procedure, is an ancient common law principle, incorporated into the Fourth Amendment, which requires law enforcement officers to announce their presence and provide residents with an opportunity to open the door prior to a search.
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.
Search incident to a lawful arrest, commonly known as search incident to arrest (SITA) or the Chimel rule, is a U.S. legal principle that allows police to perform a warrantless search of an arrested person, and the area within the arrestee’s immediate control, in the interest of officer safety, the prevention of escape, and the preservation of evidence.
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.
Schmerber v. California, 384 U.S. 757 (1966), was a landmark United States Supreme Court case in which the Court clarified the application of the Fourth Amendment's protection against warrantless searches and the Fifth Amendment right against self-incrimination for searches that intrude into the human body. Until Schmerber, the Supreme Court had not yet clarified whether state police officers must procure a search warrant before taking blood samples from criminal suspects. Likewise, the Court had not yet clarified whether blood evidence taken against the wishes of a criminal suspect may be used against that suspect in the course of a criminal prosecution.
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.
The law of search and seizure in Pennsylvania is controlled by both the United States Constitution and the broader protections of the Pennsylvania Constitution. This article is concerned only with the protections provided by the Pennsylvania Constitution.
Missouri v. McNeely, 569 U.S. 141 (2013), was a case decided by United States Supreme Court, on appeal from the Supreme Court of Missouri, regarding exceptions to the Fourth Amendment to the United States Constitution under exigent circumstances. The United States Supreme Court ruled that police must generally obtain a warrant before subjecting a drunken-driving suspect to a blood test, and that the natural metabolism of blood alcohol does not establish a per se exigency that would justify a blood draw without consent.
United States v. Watson, 423 U.S. 411 (1976), was a case decided by the Supreme Court of the United States that decided that a warrantless arrest in public and consenting to a vehicle search did not 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.
Collins v. Virginia, No. 16-1027, 584 U.S. ___ (2018), was a case before the US Supreme Court involving search and seizure. At issue was whether the Fourth Amendment's motor vehicle exception permits a police officer uninvited and without a warrant to enter private property, approach a house, and search a vehicle parked a few feet from the house that is otherwise visible from off the property. In an 8–1 judgement, the Supreme Court ruled that the automobile exception does not apply to vehicles parked within the home or the curtilage of a private homeowner.
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."
Johnson v. United States, 333 U.S. 10 (1948), was a significant United States Supreme Court decision addressing search warrants and the Fourth Amendment. In this case, where federal agents had probable cause to search a hotel room but did not obtain a warrant, the Court declared the search was "unreasonable."
Caniglia v. Strom, 593 U.S. ___ (2021), was a United States Supreme Court case related to the Fourth Amendment to the United States Constitution's "community caretaking" exception.
Lange v. California, 594 U.S. ___ (2021), was a United States Supreme Court case involving the exigent circumstances requirement related to the Fourth Amendment to the United States Constitution. The Court ruled unanimously that the warrantless entry into a home by police in pursuit of a misdemeanant is not unequivocally justified.
