Privacy Laws

Fourth Amendment


The Fourth Amendment to the U.S. Constitution protects privacy by governing how police may surveil people’s effects, including their electronic data.

The Fourth Amendment is one of the main constitutional privacy protections in the United States. The Fourth Amendment prohibits unreasonable searches and seizures without a warrant—generally, law enforcement must obtain a warrant when a search would violate a person’s “reasonable expectation of privacy.” The Fourth Amendment also requires that warrants be supported by probable cause and describe with particularity the places to be searched and persons to be seized. 

The advent of the internet and other digital technologies has ushered in new issues about when police must obtain a warrant, what must support the warrant, and what the warrant must say. Recurring questions include whether exceptions to the warrant requirement developed before cell phones and the internet apply to electronic data and the point at which police use of surveillance technology interferes with individuals’ reasonable expectation of privacy. EPIC works to ensure that advancing technology does not erode Fourth Amendment rights, primarily by participating as a “friend of the court” in important Fourth Amendment case.

Technological Advances Make Constitutional Privacy Protections More Important Than Ever — The Riley And Carpenter Decisions

In two seminal cases—Riley v. California (2014) and Carpenter v. United States (2018)—the Supreme Court has recognized that people have a reasonable expectation of privacy in the contents of their cell phone and in their historical location information. These cases show that the Court is reluctant to extend pre-digital warrant exceptions to new technological situations.

In Riley, the Court decided that the “search incident to arrest” exception to the warrant requirement did not apply to cell phones. Under the traditional search-incident-to-arrest exception, law enforcement did not need a warrant to search objects on a person being arrested because the officer’s safety during the arrest depended on ascertaining whether the objects were weapons or contained weapons. In Riley, the Supreme Court refused to expand this exception to searches of cell phones during arrests because police do not need to look at the contents of the phone to determine whether the phone is a threat to their safety. The Court found that the warrantless search of a cell phone would be an unreasonable invasion of the person’s privacy because of the vast amount of personal information it contained. 

Similarly, in Carpenter, the Court found that police needed a warrant to obtain weeks-long records of people’s movements generated by their cell phones, refusing to expand the “third-party exception” to the warrant requirement. Under the traditional third-party exception, people have no reasonable expectation of privacy in information held by a third party. In Carpenter, law enforcement attempted to use this exception to justify obtaining cell phone tower location records from the defendant’s phone carrier without first getting a warrant. The Court ruled that people have a reasonable expectation of privacy in their movements over a several weeks-long period because the information creates a revealing portrait of the person’s daily life.

EPIC’s Fourth Amendment Work

EPIC fights to ensure that our constitutional rights are not eroded by new technologies, primarily by participating as a “friend of the court” in important Fourth Amendment cases. 

EPIC has filed briefs in cases about whether school administrators may search through students’ cell phones without consent, whether the police may collect people’s DNA before they have been convicted of a crime, whether cities may compile information about people’s e-scooter rides, and whether the police may collect a person’s public transportation records without a warrant. EPIC has also intervened in cases involving the scope and methods used in searches of private information, such as whether police who have probable cause to search a cell phone for one crime may conduct a wholesale searchof the phone’s entire contents for any crimes, whether police can search electronic data automatically scanned and reported by service providers without first obtaining a warrant, and whether law enforcement may search through phones without a warrant near the border

Recent Documents on Fourth Amendment

  • Amicus Briefs

    Tuggle v. United States

    US Supreme Court

    Whether the Fourth Amendment protects against warrantless long-term, continuous, and covert pole camera surveillance of the outside of a person’s home

  • Amicus Briefs

    Sanchez v. Los Angeles Department of Transportation

    US Court of Appeals for the Ninth Circuit

    Whether compelled disclosure of detailed location information on individual e-scooter trips violates the Fourth Amendment.

  • Amicus Briefs

    United States v. Morton

    US Court of Appeals for the Fifth Circuit

    Whether law enforcement can perform an invasive forensic search of the entire contents of a phone when it only has probable cause to search some of the data on the phone.

  • Amicus Briefs

    Wisconsin v. Burch

    Wisconsin Supreme Court

    Whether a reasonable person who verbally consents to a limited search of their cell phone authorizes law enforcement to download that phone’s entire contents, store a copy of the data indefinitely, and use it in unrelated investigations based on a vague consent form.

  • Amicus Briefs

    Commonwealth v. Zachery

    Massachusetts Supreme Judicial Court

    Whether a person has a reasonable expectation of privacy in information relating to their use of a public transportation card, or in any data that card may contain or generate.

  • Amicus Briefs

    Anibowei v. Wolf

    US Court of Appeals for the Fifth Circuit

    Whether the border search exception to the Fourth Amendment warrant requirement should be extended to cell phones

  • Amicus Briefs

    Kansas v. Glover

    US Supreme Court

    Whether the Fourth Amendment allows police to stop a car when the only reason police have for the stop is that the car’s registered owner has a suspended license.

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