In a unanimous decision, the Court ruled that a physical invasion of the home is not necessary for an act to violate the search and seizure clause of the Fourth Amendment. The protection extends to the personal security of a citizen.

“It does not require actual entry upon premises and search for and seizure of papers to constitute an unreasonable search and seizure within the meaning of the Fourth Amendment.”
— Justice Joseph P. Bradley

First case where the Court considered in-depth the Fourth Amendment's reach, established the "mere evidence" rule, and set the precedent for the exclusionary rule later on.

The Court unanimously held that a warrantless seizure of private documents from the home violated the Fourth Amendment and could not be used as evidence against a citizen.

“While the efforts of courts and their officials to bring the guilty to punishment are praiseworthy, they are not to be aided by sacrificing the great fundamental rights secured by the Constitution.”
— Justice William R. Day

First application of what became known as the "exclusionary rule"

In a 7-2 decision, Justice Oliver Wendell Holmes authored the majority opinion that stated copies of records illegally seized were inadmissible in court because it would encourage police to evade the Fourth Amendment. This precedent later on became a legal metaphor known as the "fruit of the poisonous tree."

“Weeks v. United States, to be sure, had established that laying the papers directly before the grand jury was unwarranted, but it is taken to mean only that two steps are required instead of one. In our opinion, such is not the law. It reduces the Fourth Amendment to a form of words.”
— Justice Oliver Wendell Holmes

In a 7-2 decision, the Court upheld the warrantless search of an automobile, citing that its mobility made it impractical to secure a warrant because the vehicle could be moved out of the jurisdiction.

Established the “automobile exception”

In a 5-4 decision, the Court held that the use of wiretapped conversations without a warrant did not violate the Fourth Amendment because there was no physical invasion, and the party was not forcibly or illegally made to conduct the incriminating conversations.

In a 6-3 decision, the Court held that the Fourth Amendment's exclusionary rule was not applicable to the states. Though the Fourteenth Amendment prohibited unreasonable search and seizure, states were not required to exclude illegally seized evidence from trial.

Significantly limited exclusionary rule to not apply to states

In a 5-4 decision, the Court ruled that evidence obtained in violation of the Fourth Amendment did not require the exclusion of such evidence in a state court trial. Though the Court acknowledged that the police behavior "flagrantly, deliberately, and persistently violated the fundamental principle declared by the Fourth Amendment," the Fourteenth Amendment did not forbid admission of such evidence, as decided in Wolf v. Colorado.

Further limited application of Fourth Amendment in state courts and backed Wolf ruling

In a 8-1 decision, the Court ruled that a citizen subject to search and seizure, regardless of being a guest at the home rather than the property owner, has standing to challenge the constitutionality of evidence obtained and used against them.

“Distinctions such as those between 'lessee,' 'licensee,' 'invitee' and 'guest,' often only of gossamer strength, ought not to be determinative in fashioning procedures ultimately referable to constitutional safeguards.”
— Justice Felix Frankfurter

In a controversial decision, the Court ruled 6-to-3 that all evidence obtained by search and seizure in violation of the Fourth Amendment was inadmissible in a state court. This historic decision launched the Court on a troubled course of determining how and when to apply the exclusionary rule.

T“o hold otherwise is to grant the right but, in reality, to withhold its privilege and enjoyment.”
— Justice Tom C. Clark

Historic and controversial ruling that extended Fourth Amendment and exclusionary rule to apply to all level of government.

In a 5-4 vote, the Court held that unannounced entry by police to conduct a warrantless search based upon reasonable suspicion is not illegal. Therefore, contraband obtained in plain-view could be admitted as evidence. Following Mapp v. Ohio, this decision gave further guidance on when evidence was considered fruit from an unlawful search or seizure.

Expansion of police power

As a follow-up to Mapp v. Ohio, the Court held 7-to-2 that the exclusionary rule does not apply retroactively. The Court set out that the exclusionary rule was meant to deter police action, and applying the Mapp decision to previous police misconduct would threaten the "delicate state-federal relationship."

Narrowed the foundation of the exclusionary rule

In a 8-1 decision, the Court rejected the "mere evidence" rule established by Boyd v. United States that stated items seized only to be used as evidence against the property owner violated the Fourth Amendment. In doing so, the Court relied more on the distinction between testimonial evidence and physical evidence rather than mere evidence and instrumentalities by which the crime was committed.

“We have recognized that the principal object of the Fourth Amendment is the protection of privacy, rather than property, and have increasingly discarded fictional and procedural barriers rested on property concepts.”
— Justice Brennan

In a 7-1 decision, the Court ruled that a warrantless recording of conversations violated the Fourth Amendment and that a physical intrusion was not necessary to constitute a search. A concurring opinion by Justice John Marshall Harlan introduced the idea of a "reasonable expectation of privacy."

“The Fourth Amendment protects people, not places.”
— Justice Potter Stewart

Established "reasonable expectation of privacy"

In a 8-1 decision, the Court held that police may stop and frisk an individual without a warrant if the officer has a reasonable suspicion the person is committing, or about to commit a crime. The Court balanced the need for police protection against the nature of intrusion.

“The exclusionary rule has its limitations, however, as a tool of judicial control. It cannot properly be invoked to exclude the products of legitimate police investigative techniques on the ground that much conduct which is closely similar involves unwarranted intrusions upon constitutional protections. - Chief Justice Earl Warren; To give the police greater power than a magistrate is to take a long step down the totalitarian path. Perhaps such a step is desirable to cope with modern forms of lawlessness. But if it is taken, it should be the deliberate choice of the people through a constitutional amendment.”
— Justice WIlliam O. Douglas in his dissent

Limited exclusionary rule; established "stop and frisk" right

In a 7-2 decision, the Court held that searches "incident to arrest" are limited to the area within immediate control of the suspect. The Court emphasized the importance of warrants and probable cause as necessary bulwarks against government abuse.

“Such searches, in the absence of well recognized exceptions, may be made only under the authority of a search warrant. The "adherence to judicial processes" mandated by the Fourth Amendment requires no less.”
— Justice Potter Stewart

Limited prior Court precedent that permitted searches far beyond the arrestee's grabbing area

In a 5-3 decision, the Court held that the exclusionary rule applied to conversations unlawfully overheard by the government. An individual thus has standing to object so these surveillance records be turned over to him without being seen by a trial judge.

In a 7-1 decision, the Court applied the Carroll doctrine to permit the warrantless search of an automobile after it was moved to the police station following an arrest.

Expansion of police power

In a 5-4 decision, of which many justices chose to concur in part and dissent in part, the Court ruled the seizure of evidence from the suspect's automobile was invalid because a neutral magistrate had not issued the warrant. However, Justice Black's dissent, joined by Justice Blackmun, stated that "the Fourth Amendment supports no exclusionary rule."

“The most basic constitutional rule in this area is that 'searches conducted outside the judicial process, without prior approval by judge or magistrate, are per se unreasonable under the Fourth Amendment -- subject only to a few specifically established and well delineated exceptions. The exceptions are "jealously and carefully drawn.'”
— Justice Potter Stewart

In a 6-3 decision, the Court ruled a full search of a person conducted during a lawful arrest is reasonable under the Fourth Amendment.

Expansion of police power

In a 5-4 decision, the Court established the "co-occupant consent rule" in and held that police may search a residence upon voluntary consent of a third party who possess authority over the common area.

In a 5-4 decision, the Court ruled any items collected during a warrantless search incident to arrest or incarceration can be used as evidence against the arrestee.

Expansion of police power

The Court ruled 6-to-2 that evidence found during a warrantless search of an automobile after arrest was admissible.

Expansion of police power

In a 6-3 decision, Justice Powell in the majority opinion wrote that federal courts were not obligated to consider claims of illegal searches and seizure after such claims had been decided by state courts, as the Constitution did not require granting of federal habeas corpus relief. The Court found that the exclusionary rule would not be enhanced in such instances and deterrence of police misconduct was unlikely to increase.

“It seems clear to me that the exclusionary rule has been operative long enough to demonstrate its flaws. The time has come to modify its reach, even if it is retained for a small and limited category of cases.” — Chief Justice Warren E. Burger, writing in concurrence;
“We do reaffirm that the exclusionary rule is a judicially created remedy, rather than a personal constitutional right.”
— Justice Lewis F. Powell, Jr.

In a 7-2 decision, the Court ruled that a warrantless search of locked luggage within a parked vehicle was not permissible under the "automobile exception." Luggage does not have the lessened expectation of privacy, as does an automobile.

Starts to limit "automobile exception"

In a 5-4 decision, the Court held that passengers in a car of which they did not own had no "legitimate expectation of privacy." Then-Associate Justice Rehnquist wrote in his majority opinion that to allow any party "legitimately on premises" where the search occurred to challenge its constitutionality, a precedent established by Jones v. United States, was too broad.

“We would not wish to be understood as saying that legitimate presence on the premises is irrelevant to one's expectation of privacy, but it cannot be deemed controlling.”
— Justice William Rehnquist

Narrowed scope of expectation of privacy set out in Jones v. United States and Katz v. United States

In a 6-3 decision, the Court ruled conditions faced by detainees prior to conviction, such as body cavity searches and shakedowns, do not violate the Fourth Amendment.

The Court ruled 5-to-3 that the installation and use of a pen register, an electronic device used to record all numbers called from a phone line, does not constitute a search under the Fourth Amendment. A reasonable expectation of privacy does not apply because the petitioner "voluntarily conveyed" those numbers to the telephone company.

“It is too much to believe that telephone subscribers, under these circumstances, harbor any general expectation that the numbers they dial will remain secret.”
— Justice Harry Blackmun

In a 6-3 decision, the Court ruled a New York statute that authorized warrantless search and seizure violated the Fourth Amendment. In the absence of special circumstances, entry into a private home required a warrant.

EEstablished that the home is entitled more protection than an automobile

The Court ruled in a 6-to-3 decision that police may also search the passenger compartment of a vehicle upon lawful arrest of the vehicle's occupant.

Extended Chimel rule

In a 6-3 decision, the Court held that a warrantless search of a vehicle's trunk, which included closed containers, did not violate the Fourth Amendment because police acted with probable cause.

Expansion of police power with automobile exception

In a 6-3 decision, the Court upheld a search based on an anonymous tip, establishing that the "totality-of-the-circumstances" should be considered when determining probable cause.

In a 5-4 decision, the Court held that protection against unreasonable searches under the Fourth Amendment did not apply "within the confines of the prison cell." Chief Justice Burger wrote in his majority opinion that "the paramount interest in institutional security" outweighed all privacy concerns.

Expansion of state power in prison

In a 6-3 decision, the Court held evidence seized on a mistakenly issued warrant was permissible because of a "good faith" exception. The exclusionary rule, argued the majority, was not a right but a remedy to deter illegal police conduct.

The substantial social costs exacted by the exclusionary rule for the vindication of Fourth Amendment rights have long been a source of concern.
— Justice Byron R. White

Limited exclusionary rule

In a 5-4 decision, the Court ruled that a warrantless search of a probationer's home did not violate the Fourth Amendment. A person committed to legal custody is subject to that department's rules and regulations.

Expansion of police power

In a 5-4 decision, the Court held the exclusionary rule does not apply to evidence obtained by police who were acting in "good faith" of a state statute later held invalid. The state statute permitted police to conduct warrantless administrative searches.

“[T]o the extent that application of the exclusionary rule could provide some incremental deterrent, that possible benefit must be weighed against [its] substantial social costs.”
— Justice Harry Blackmun

In a 7-2 decision, the Court ruled that a limited protective sweep of a home upon arrest is permissible if the officer has a reasonable belief the area may pose a threat. Justice White, writing for the majority, relied on the balance set forth in Terry v. Ohio between the need for officer security and the nature of intrusion.

Expansion of police power

In a 6-3 decision, the Court held a search valid that was conducted by police upon third party consent, who did not own the apartment. Since the Fourth Amendment is based on "reasonable" searches rather than consent, it was "reasonable" for police to believe the third party had authority over the premises.

“But 'reasonableness,'' with respect to this necessary element, does not demand that the government be factually correct in its assessment that that is what a search will produce. Warrants need only be supported by 'probable cause,'' which demands no more than a proper 'assessment of probabilities in particular factual contexts ....'”
— Justice Antonin Scalia

Expansion of search and police power

In a 6-3 decision, the Court held that the "automobile exception" was broad enough to permit the warrantless search of a container within a car if police have probable cause it contains evidence. The ruling thus interpreted Carroll as providing one rule to govern all automobile searches -- "police may search an automobile and the containers within it where they have probable cause to believe contraband or evidence is contained."

“Until today, this Court has drawn a curious line between the search of an automobile that coincidentally turns up a container and the search of a container that coincidentally turns up in an automobile. The protections of the Fourth Amendment must not turn on such coincidences.”
— Justice Harry Blackmun

Expansion of search, police power, and broadening of automobile exception

In a unanimous decision, the Court ruled that absent a search or arrest, seizure of one's property implicates the Fourth Amendment. The Fourth Amendment protects property as well as privacy interests, and in this case, the seizure of a mobile home during an eviction violates one's property rights.

In a 7-2 decision, the Court ruled the exclusionary rule does not apply to evidence obtained through a warrantless search when a police record mistakenly indicates an outstanding warrant due to personnel error.

Expanded upon Leon, where there had been a presumably valid warrant issued at the time of the case

A unanimous Court ruled police must "knock and announce" before entering a house. Officer safety, however, may establish the reasonableness of an unnanounced entry if at risk.

“Given the longstanding common-law endorsement of the practice of announcement, and the wealth of founding-era commentaries, constitutional provisions, statutes, and cases espousing or supporting the knock-and-announce principle...the Amendment's Framers thought that whether officers announced their presence and authority before entering a dwelling was among the factors to be considered in assessing a search's reasonableness.”
— Justice Clarence Thomas

Limited police power

In an unanimous decision, the Court ruled any traffic violation gave police legal basis for a stop.

“[W]e have been unwilling to entertain Fourth Amendment challenges based on the actual motivations of individual officers.”
— Justice Antonin Scalia

Expansion of police power

In a 5-4 decision, the Court held the exclusionary rule does not apply to parole revocation hearings. In the majority opinion, Justice Thomas argued the exclusionary rule is not constitutionally mandated and only applies when its deterrent benefits outweigh social costs of excluding reliable evidence.

“[T]he rule’s costly toll upon truth-seeking and law enforcement objectives presents a high obstacle for those urging [its] application.”
— Justice Clarence Thomas

Limited exclusionary rule

In a 6-3 decision, the Court held that so long as there is probable cause to search a stopped vehicle, all subsequent searches of its contents are legal as well. The Court added that such searches are especially warranted if aimed at looking into objects or personal belongings capable of concealing items that are the object of the search.

“Where [Fourth Amendment] inquiry yields no answer, we must evaluate the search or seizure under traditional standards of reasonableness by assessing, on the one hand, the degree to which it intrudes upon an individual's privacy and, on the other, the degree to which it is needed for the promotion of legitimate governmental interests.”
— Justice Antonin Scalia

Expansion of police power and automobile exception

In a 7-2 decision, the Court ruled that physical manipulation of an individual's carry-on luggage by law enforcement counted as an unreasonable search and thus violated the Fourth Amendment.

“We cannot sanction stops justified only by the generalized and ever-present possibility that interrogation and inspection may reveal that any given motorist has committed some crime.”
— Justice Sandra Day O'Connor

In a 6-3 decision, the Court held that highway checkpoints with the intent to intercept illegal drugs violated the Fourth Amendment.

In a 8-1 decision, the Court ruled officers may detain an individual from entering the home while they await a warrant so as to prevent the destruction of evidence.

In a 5-4 decision, the Court ruled that the use of thermal imaging on a private home counted as an unconstitutional search in violation of the Fourth Amendment.

“[W]here, as here, the Government uses a device that is not in general public use, to explore details of the home that would previously have been unknowable without physical intrusion, the surveillance is a 'search' and is presumptively unreasonable without a warrant.”
— Justice Antonin Scalia

A unanimous Court ruled a warrantless search of an individual on probation was supported by reasonable suspicion and authorized as a condition of parole. The Court then concluded that based on ordinary Fourth Amendment analysis, reasonable suspicion is constitutionally sufficient to render a warrant requirement unnecessary.

Limited warrant requirements

In a 6-3 decision, the Court held the Fourth Amendment does not require police to inform bus passengers of their rights to refuse consent to searches.

In a 7-2 decision, the Court held that police may search the vehicle of a person they have arrested if they did not make contact with him until after he left the vehicle.

In a 5-4 decision, the Court upheld Hiibel's arrest and conviction under a state statute for not telling police his name while the officer was investigating an assault. The Court ruled that the search did not violate the Fourth Amendment because the officer had reasonable cause and asking a party's name involved only a minimally intrusive question.

In a 5-3 decision, the Court held that when two occupants are present and one consents to a search while the other objects, police may not search the home.

“The constant element in assessing Fourth Amendment reasonableness in the consent cases, then, is the great significance given to widely shared social expectations, which are naturally enough influenced by the law of property, but not controlled by its rules.”
— Justice David H. Souter

Limited police power

In a 8-0 decision, the Court ruled police may enter a building without a warrant if there is reasonable basis that an occupant is seriously injured or threatened with such injury.

“Nevertheless, because the ultimate touchstone of the Fourth Amendment is 'reasonableness,' the warrant requirement is subject to certain exceptions.”
— Chief Justice John G. Roberts, Jr.

Expansion of police power

In a 5-4 decision, the Court ruled that the exclusionary rule does not apply to evidence obtained in violation of the "knock-and-announce" rule, established by Wilson v. Arkansas.

“The exclusionary rule generates 'substantial social costs,' ... which sometimes include setting the guilty free and the dangerous at large. We have therefore been 'cautio[us] against expanding' it.”
— Justice Antonin Scalia

Limited knock-and announce, limited exclusionary rule, and increased police power

In a 6-3 decision, the Court affirmed suspicion-less searches of parolees. An individual still under custody of a correctional facility has significantly reduced privacy rights, therefore no warrant or suspicion is needed to constitute a lawful search under the Fourth Amendment.

“The extent and reach of these conditions clearly demonstrate that parolees like petitioner have severely diminished expectations of privacy by virtue of their status alone.”
— Justice Clarence Thomas

Expansion of police power and limited rights of parolees

In a 5-4 decision, the Court held that evidence obtained under a mistakenly issued warrant is admissible in court and not subject to the exclusionary rule.

“[W]hen police mistakes are the result of negligence such as that described here, rather than systemic error or reckless disregard of constitutional requirements, any marginal deterrence does not 'pay its way.'”
— John G. Roberts, Jr.

Expansion of police power

In a 5-4 decision, the Court ruled that police may search the vehicle of its recent occupant after arrest only if it is reasonable to believe that the arrestee might access the vehicle at the time of the search or that the vehicle contains evidence of the offense of the arrest.

Limited police power and automobile exception

A unanimous Court held that the City of Ontario did not violate its employees' Fourth Amendment rights by reviewing text messages on a city-issued pager. The search was a reasonable work-related audit that was not excessive in scope.

A unanimous Court ruled that the warrantless use of a GPS tracking device on a vehicle violated the Fourth Amendment.

Limited police power

In a 5-4 decision, the Court held that prison officials may conduct a suspicion-less strip search whenever an individual is arrested before entering the general prison population, including for minor offenses.

Increased power of state officials

In a unanimous decision, the Court ruled a drug-detection dog's alert established probable cause for an officer to conduct a warrantless search of a vehicle.

Expansion of police power

In a 5-4 decision, the Court held the use of a detection dog to sniff for drugs at the front door of a house constituted a search under the Fourth Amendment, and thus required probable cause or a search warrant.

“We therefore regard the area 'immediately surrounding and associated with the home'—what our cases call the curtilage—as 'part of the home itself for Fourth Amendment purposes' ... That principle has ancient and durable roots.”
— Justice Antonin Scalia

Limited police power

In a 8-1 decision, the Court ruled that taking a warrantless blood sample of a drunk-driver suspect violated the Fourth Amendment.

In a 5-4 decision, the Court held that a DNA swab test as a part of the arrest procedure does not violate the Fourth Amendment. It serves a legitimate state interest and is not so invasive so as to require a warrant.

In a 6-3 decision, the Court ruled that a warrantless search is reasonable when the tenant, who previously objected, is no longer present and the co-tenant consents. Because the objecting tennant was arrested, the Court held the co-tenant had authority to consent to a search.

A unanimous Court ruled that a warrantless search of a cell phone upon arrest counted as unreasonable search and seizure. The Court argued the warrantless search exception existed to protect officer safety and preserve evidence. Digital data could not be used to harm the officer and its contents could be preserved.

Justice Alito called the Chimel reasoning as "questionable", writing “I think it is a mistake to allow that reasoning to affect cases like these that concern the search of the person of arrestees.”

Limited police power