Katz v. U.S.: Safeguarding Privacy Against Modern Technologies

We once kept private documents at home—now, we carry our bank accounts, medical records, and private messages everywhere on our mobile phones. The Fourth Amendment, ratified in 1791, protects the right of people “to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.”[1] But the Framers of the Constitution never had telephones. They never knew about wiretapping, infrared scanning, or GPS tracking. So how does the Fourth Amendment protect us from “unreasonable searches and seizures”[2] in modern-day society?

To answer this question, let us examine how the Supreme Court case Katz v. U.S. (1967) revolutionized Fourth Amendment interpretation. Prior to Katz, the Supreme Court defined a “search” under the “trespass” doctrine. This property-based view was ill-suited to dealing with evolving technologies. The Katz decision, however, safeguarded Fourth Amendment protections by making privacy a key tenet of Fourth Amendment jurisprudence.

Before Katz, “search and seizure” applied primarily to tangible objects: a person’s body, their home, their papers, and their material belongings.[3] Physical papers were protected, while intangible communications such as phone calls, for instance, were not. This so-called “trespass” doctrine was adopted by the Supreme Court in Olmstead v. U.S. (1928), where the Supreme Court allowed the government to wiretap telephone lines and eavesdrop on private telephone calls without a warrant.

This “trespass” doctrine was the controlling precedent until the 1960s, when it was seriously challenged by another idea, that is, the right to privacy. Katz v. U.S (1967) brought privacy to the forefront of Fourth Amendment jurisprudence.

The relevant Katz facts were straightforward. In February of 1965, the petitioner Charles Katz used a public telephone to illegally place bets and wagers across state lines.[4] The FBI used a listening device, which was attached to the outside of the telephone booth,[5] to discreetly make recordings of Katz’s telephone conversations. These recordings eventually helped secure a criminal conviction against Katz. By 1967, Katz had appealed his case to the Supreme Court. He claimed that the FBI had violated his Fourth Amendment rights.

While Katz’s facts were clear, its legal arguments presented the Supreme Court with a Constitutional dilemma. Times had changed, and the Supreme Court had begun to appreciate the central role that the public telephone had taken in transmitting “private communication.”[6] From this perspective, the FBI had clearly violated Katz’s expectation of privacy.

Yet, the telephone booth was public property, and Katz’s conversation was not a tangible object to be searched or seized. Hence, according to the “trespass” doctrine, the listening device would not have encroached upon Katz’s Fourth Amendment rights. A subjective expectation of privacy was of little concern to the “trespass” doctrine.

When initially considering the case, “the justices...split four to four at conference”[7] and were unable to decide how to rule. Justice Potter Stewart, however, had his law clerk Laurence Tribe prepare a memorandum, which would—with some revisions—eventually break the Supreme Court stalemate.[8] 

By the end of deliberations, the Court had split seven to one. The majority agreed that Katz’s Fourth Amendment rights had been violated. Justice Stewart, who wrote the majority opinion, argued that what someone “seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.”[9] Here, he coined his well-known phrase that the Fourth Amendment “protects people—and not simply areas.”[10] 

Justice Stewart’s arguments changed the direction of Fourth Amendment jurisprudence. For the first time, an intention to keep something private—rather than a property-based “trespass” doctrine—became an important factor to defining a Fourth Amendment “search.” A person’s private affairs could be protected even on public land, especially when the effects of technologies like the telephone were considered.

The Katz majority opinion laid the foundation for safeguarding privacy against modern technology. But exactly what sort of privacy does the Fourth Amendment protect? Privacy is different for everyone: While one person may be comfortable with satellite imagery, another person may liken Google Maps to 1984’s Big Brother surveillance. Recognizing the need to clarify “privacy” under the Fourth Amendment, Justice John Marshall Harlan, in his concurring opinion in Katz, created a “reasonable expectation of privacy” test. The test has two prongs: 1) The person must exhibit an “actual (subjective) expectation of privacy”[11] and 2) society recognizes the expectation as “reasonable.”[12] If the government violates these criteria against an individual, then a “search” (in the Fourth Amendment sense) has been conducted by the government.

Still, the meaning of privacy under Katz’s “reasonable expectation of privacy” test is vague: What is reasonable? Who gets to define the “reasonable” expectation? Yet, by incorporating the explicit notion of “reasonable expectation of privacy” into Fourth Amendment interpretation, the Supreme Court gave itself the tools to deal with changing technologies.  

The Katz test continues to prove relevant to recent Supreme Court cases. Since Katz, the Supreme Court has heard cases involving technologies ranging from GPS tracking to aerial photography. Because of the Katz test, the government, for example, must obtain a warrant to scan your home with a thermal imaging device[13] and to track your location through cell phone tower data.[14] While the “trespass” doctrine may have allowed government intrusions of privacy with these two technologies, the “reasonable expectation of privacy” requirement ensures that your privacy is protected.

The Framers of the Constitution may not have had mobile phones, cars with GPS devices, or the Internet—but the Supreme Court justices do. The justices acknowledge the changing meaning of both privacy and the Fourth Amendment as technology advances. The Katz “reasonable expectation of privacy test” will continue to keep your private conversations, location data, and homes safe from “unreasonable searches,” even as times change and modern technologies evolve.

Jaehyun Hong is a current first-year who plans to study Philosophy. She is a Staff Writer of the Law Review's Blog and can be reached at jaehyun_hong@brown.edu.

References

Brittany Boatman, “United States v. United States v. Jones: The Foolish revival of the ‘Trespass Doctrine

Doctrine’ in Addressing GPS Technology and the Fourth Amendment,” Valparaiso University Law Review, https://scholar.valpo.edu/cgi/viewcontent.cgi?article=2292&context=vulr, 680.

Carpenter v. United States, 585 U.S. ___ (2018).

David O’Brien, Constitutional Law and Politics: Civil Rights and Civil Liberties, Volume Two, Tenth Edition 

(New York: W.W. Norton & Company, 2017), 950.

“Katz v. United States,” Oyez, Cornell’s Legal Information Institute (LII), Justia, and Chicago-Kent College

of Law, www.oyez.org/cases/1967/35.

Katz v. United States, 389 U.S. 347 (1967).

Kyllo v. United States, 533 U.S. 27 (2001).

U.S. Const. amend. IV.

[1] U.S. Const. amend. IV.

[2] Ibid.

[3] Brittany Boatman, “United States v. Jones: The Foolish revival of the ‘Trespass Doctrine Doctrine’ in Addressing GPS Technology and the Fourth Amendment,” Valparaiso University Law Review, https://scholar.valpo.edu/cgi/viewcontent.cgi?article=2292&context=vulr, 680. 

[4] Katz v. United States, 389 U.S. 347 (1967). Syllabus.

[5] “Katz v. United States,” Oyez, Cornell’s Legal Information Institute (LII), Justia, and Chicago-Kent College of Law, www.oyez.org/cases/1967/35.

[6] Katz v. United States, 389 U.S. 347 (1967). Majority opinion written by Justice Stewart. Emphasis added.

[7] David O’Brien, Constitutional Law and Politics: Civil Rights and Civil Liberties, Volume Two, Tenth Edition (New York: W.W. Norton & Company, 2017), 950. Justice Thurgood Marshall recused himself.

[8] Ibid.

[9] Katz v. United States, 389 U.S. 347 (1967). Majority opinion written by Justice Stewar[a]t.

[10] Ibid.

[11] Katz v. United States, 389 U.S. 347 (1967). Concurring opinion written by Justice Harlan.

[12] Ibid.

[13] Kyllo v. United States, 533 U.S. 27 (2001).

[14] Carpenter v. United States, 585 U.S. ___ (2018).