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.
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.
The open-fields doctrine, in the U.S. law of criminal procedure, is the legal doctrine that a "warrantless search of the area outside a property owner's curtilage" does not violate the Fourth Amendment to the United States Constitution. However, "unless there is some other legal basis for the search," such a search "must exclude the home and any adjoining land that is within an enclosure or otherwise protected from public scrutiny."
Katz v. United States, 389 U.S. 347 (1967), was a landmark decision of the U.S. Supreme Court in which the Court redefined what constitutes a "search" or "seizure" with regard to the protections of the Fourth Amendment to the U.S. Constitution. The ruling expanded the Fourth Amendment's protections from an individual's "persons, houses, papers, and effects", as specified in the Constitution's text, to include any areas where a person has a "reasonable expectation of privacy". The reasonable expectation of privacy standard, now known as the Katz test, was formulated in a concurring opinion by Justice John Marshall Harlan II.
Florida v. Riley, 488 U.S. 445 (1989), was a United States Supreme Court decision which held that police officials do not need a warrant to observe an individual's property from public airspace.
California v. Greenwood, 486 U.S. 35 (1988), was a case in which the Supreme Court of the United States held that the Fourth Amendment does not prohibit the warrantless search and seizure of garbage left for collection outside the curtilage of a home.
Kyllo v. United States, 533 U.S. 27 (2001), was a decision by the Supreme Court of the United States in which the court ruled that the use of thermal imaging devices to monitor heat radiation in or around a person's home, even if conducted from a public vantage point, is unconstitutional without a search warrant. In its majority opinion, the court held that thermal imaging constitutes a "search" under the Fourth Amendment, as the police were using devices to "explore details of the home that would previously have been unknowable without physical intrusion." The ruling has been noted for refining the reasonable expectation of privacy doctrine in light of new surveillance technologies, and when those are used in areas that are accessible to the public. This case has been praised by legal scholars since the Court refused to be the arbiter to determine "what is and is not intimate" and thus worthy of protection. Instead, the Court opted to focus on "the invasiveness of the technology itself" and its ability to enable all kinds of government surveillance in the home.
In United States constitutional law, expectation of privacy is a legal test which is crucial in defining the scope of the applicability of the privacy protections of the Fourth Amendment to the U.S. Constitution. It is related to, but is not the same as, a right to privacy, a much broader concept which is found in many legal systems. Overall, expectations of privacy can be subjective or objective.
Smith v. Maryland, 442 U.S. 735 (1979), was a Supreme Court case holding that the installation and use of a pen register by the police to obtain information on a suspect's telephone calls was not a "search" within the meaning of the Fourth Amendment to the United States Constitution, and hence no search warrant was required. In the majority opinion, Justice Harry Blackmun rejected the idea that the installation and use of a pen register constitutes a violation of the suspect's reasonable expectation of privacy since the telephone numbers would be available to and recorded by the phone company anyway.
Oliver v. United States, 466 U.S. 170 (1984), is a United States Supreme Court decision relating to the open fields doctrine limiting the Fourth Amendment to the United States Constitution.
California v. Ciraolo, 476 U.S. 207 (1986), was a decision by the Supreme Court of the United States in which the Court held that aerial observation of a person's backyard by police, even if done without a search warrant, does not violate the Fourth Amendment to the U.S. Constitution.
The Stored Communications Act is a law that addresses voluntary and compelled disclosure of "stored wire and electronic communications and transactional records" held by third-party Internet service providers (ISPs). It was enacted as Title II of the Electronic Communications Privacy Act of 1986 (ECPA).
United States v. Knotts, 460 U.S. 276 (1983), was a United States Supreme Court case regarding the use of an electronic surveillance device. The defendants argued that the use of this device was a Fourth Amendment violation. The device in question was described as a beeper that could only be tracked from a short distance. During a single trip, officers followed a car containing the beeper, relying on beeper signal to determine the car's final destination. The Court unanimously held that since the use of such a device did not violate a legitimate expectation of privacy there was no search and seizure and thus the use was allowed without a warrant. It reasoned that a person traveling in public has no expectation of privacy in one's movements. Since there was no search and seizure there was not a Fourth Amendment violation.
United States v. Jones, 565 U.S. 400 (2012), was a landmark United States Supreme Court case in which the court held that installing a Global Positioning System (GPS) tracking device on a vehicle and using the device to monitor the vehicle's movements constitutes a search under the Fourth Amendment.
United States v. Graham, 846 F. Supp. 2d 384, was a Maryland District Court case in which the Court held that historical cell site location data is not protected by the Fourth Amendment. Reacting to the precedent established by the recent Supreme Court case United States v. Jones in conjunction with the application of the third party doctrine, Judge Richard D. Bennett found that "information voluntarily disclosed to a third party ceases to enjoy Fourth Amendment protection" because that information no longer belongs to the consumer, but rather to the telecommunications company that handles the transmissions records. The historical cell site location data is then not subject to the privacy protections afforded by the Fourth Amendment standard of probable cause, but rather to the Stored Communications Act, which governs the voluntary or compelled disclosure of stored electronic communications records.
The third-party doctrine is a United States legal doctrine that holds that people who voluntarily give information to third parties—such as banks, phone companies, internet service providers (ISPs), and e-mail servers—have "no reasonable expectation of privacy" in that information. A lack of privacy protection allows the United States government to obtain information from third parties without a legal warrant and without otherwise complying with the Fourth Amendment prohibition against search and seizure without probable cause and a judicial search warrant.
The mosaic theory is a legal doctrine in American courts for considering issues of information collection, government transparency, and search and seizure, especially in cases involving invasive or large-scale data collection by government entities. The theory takes its name from mosaic tile art: while an entire picture can be seen from a mosaic's tiles at a distance, no clear picture emerges from viewing a single tile in isolation. The mosaic theory calls for a cumulative understanding of data collection by law enforcement and analyzes searches "as a collective sequence of steps rather than individual steps."
Carpenter v. United States, 585 U.S. 296 (2018), is a landmark United States Supreme Court case concerning the privacy of historical cell site location information (CSLI). The Court held that the government violates the Fourth Amendment to the United States Constitution when it accesses historical CSLI records containing the physical locations of cellphones without a search warrant.
United States v. Miller, 425 U.S. 435 (1976), was a United States Supreme Court that held that bank records are not subject to protection under the Fourth Amendment to the United States Constitution. The case, along with Smith v. Maryland, established the principle of the third-party doctrine in relation to privacy rights.
The aerial surveillance doctrine is the legal doctrine in the United States of America that under the Fourth Amendment, aerial surveillance of an individual’s property does not inherently constitute a search for which law enforcement must obtain a warrant. Courts have used several factors–sometimes only one or a few, other times many or all of them–to determine whether the surveillance in question is a search in violation of one’s constitutional rights: the object of the surveillance, the technology employed, the duration of the surveillance, scope of aggregated information, and the vantage point from which the surveillance is conducted.
