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Katz v. United States

Katz v. United States is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Katz v. United States rather than just read about it. In short: Katz v. United States, 389 U.S. 347 (1967), is a landmark decision of the U.S.

Katz v. United States — main illustration
Katz v. United States — illustration

Key takeaways

  • Katz v. United States belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Katz v. United States to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Katz v. United States from memory before moving on to harder problems.

Reference excerpt

Katz v. United States, 389 U.S. 347 (1967), is a landmark decision of the U.S. Supreme Court in which the Court redefined what constitutes a "search" or "seizure" with regard to 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. The Katz test has since been used in numerous cases, particularly because of technological advances that create new questions about privacy norms and government surveillance of personal data.

Background Charles Katz was a sports bettor who by the mid-1960s had become "probably the preeminent college basketball handicapper in America". In 1965, Katz regularly used a public telephone booth near his apartment on Sunset Boulevard in Los Angeles to communicate his gambling handicaps to bookmakers in Boston and Miami. Unbeknownst to him, the FBI had begun investigating his gambling activities and was recording his conversations via a covert listening device attached to the outside of the phone booth. After recording many of his phone calls, FBI agents arrested Katz and charged him with eight counts of knowingly transmitting wagering information by telephone between U.S. states, which is a federal crime under Section 18 of the United States Code, particularly a law on the transmission of wagering information. Katz was tried in the U.S. District Court for the Southern District of California. Katz moved to suppress the FBI's recordings, arguing that because the agents did not have a search warrant allowing them to place their listening device, the recordings had been made in violation of the Fourth Amendment and should be inadmissible in court per the exclusionary rule. The judge denied Katz's motion and held that the recordings were admissible as evidence, and Katz was convicted based on them. Katz appealed his conviction to the U.S. Court of Appeals for the Ninth Circuit. In 1966, the Ninth Circuit affirmed Katz's conviction, ruling that because the FBI's eavesdropping device did not physically penetrate the telephone booth's wall, no Fourth Amendment search occurred, and so the FBI did not need a warrant to place the device. Katz then appealed to the Supreme Court, which granted certiorari.

Opinion of the court On December 18, 1967, the Supreme Court issued a 7–1 decision in favor of Katz that invalidated the FBI's wiretap evidence and overturned Katz's criminal conviction. The majority opinion was written by Justice Potter Stewart. The Court began by dismissing the parties' characterization of the case in terms of a traditional trespass-based analysis that hinged on, first, whether the public telephone booth Katz had used was a "constitutionally protected area" where he had a "right of privacy"; and second, on whether the FBI had "physically penetrated" the protected area and thus violated the Fourth Amendment. Instead, the Court viewed the situation through the lens of how Katz's use of the phone booth would be perceived by himself and then objectively by others. In an oft-cited passage, Stewart wrote:

The petitioner [Katz] has strenuously argued that the booth was a "constitutionally protected area." The Government has maintained with equal vigor that it was not. But this effort to decide whether or not a given "area," viewed in the abstract, is "constitutionally protected" deflects attention from the problem presented by this case. For the Fourth Amendment protects people, not places. What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected. The Supreme Court then surveyed the history of American jurisprudence on governmental searches and seizures. It described how American courts had traditionally analyzed Fourth Amendment searches by comparing them to the long-established doctrine of trespass. In their legal briefs, the parties had focused on the 1928 precedent Olmstead v. United States, in which the Court ruled that surveillance by wiretap without any trespass did not constitute a "search" for Fourth Amendment purposes. However, the Court stated that in later cases it had begun recognizing that the Fourth Amendment applied to recorded speech obtained without any physical trespassing, and that the law had evolved. Stewart wrote:

We conclude that the underpinnings of Olmstead [and similar cases] have been so eroded by our subsequent decisions that the "trespass" doctrine there enunciated can no longer be regarded as controlling. The Government's activities in electronically listening to and recording the petitioner's words violated the privacy on which he justifiably relied while using the telephone booth and thus constituted a "search and seizure" within the meaning of the Fourth Amendment. Stewart then concluded the Court's opinion by ruling that even though the FBI knew there was a "strong probability" that Katz was breaking the law when using the phone booth, their use of the wiretap was an unconstitutional search because they did not obtain a warrant before placing the listening device. This overturned Katz's criminal conviction as a constitutional violation.

Harlan's concurrence

Justice John Marshall Harlan II's concurring opinion in Katz has become more influential than the majority opinion. The concurrence introduced a two-part test that has come to be known as the Katz test. Harlan began his opinion by noting that he was writing separately to elaborate on the meaning of Stewart's majority opinion. Harlan explained that he interpreted Stewart's statements that "the Fourth Amendment protects people, not places" and "what a person knowingly exposes to the public [...] is not a subject of Fourth Amendment protection" to mean that the Fourth Amendment is activated any time a person has a reasonable expectation of privacy in the eyes of society at large. He summarized his view of the law as comprising a two-part test:

… excerpt ends here. Continue reading the full article.

Illustrations

Katz v. United States: Justice Potter Stewart, who authored the Court's opinion in Katz
Justice Potter Stewart, who authored the Court's opinion in Katz
Katz v. United States: Justice John Marshall Harlan II, whose concurring opinion created the two-part "Katz test" that is regularly applied in Fourth Amendment cases
Justice John Marshall Harlan II, whose concurring opinion created the two-part "Katz test" that is regularly applied in Fourth Amendment cases

Worked examples

Example 1 — a first encounter with Katz v. United States

Start with the simplest possible case. Write down what Katz v. United States claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Katz v. United States before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Katz v. United States ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Katz v. United States

In research
Katz v. United States appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Katz v. United States in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Katz v. United States is common in secondary-school and first-year university syllabi. It links to neighbouring topics 20th-century American trials, Gambling in the United States, History of Los Angeles, so understanding it makes those chapters shorter.
In everyday life
Look for Katz v. United States outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Katz v. United States in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Katz v. United States means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Katz v. United States out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Katz v. United States in simple terms?

Katz v. United States, 389 U.S. 347 (1967), is a landmark decision of the U.S.

Why does Katz v. United States matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Katz v. United States?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Katz v. United States.

Tags

  • 20th-century American trials
  • Gambling in the United States
  • History of Los Angeles
  • Privacy of telecommunications
  • Public phones
  • Trials in California
  • United States Supreme Court cases
  • United States Supreme Court cases in 1967
  • United States Supreme Court cases of the Warren Court
  • United States Supreme Court decisions that overrule a prior Supreme Court decision
  • United States privacy case law
  • United States search case law

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