Fourth Amendment

The Supreme Court's 'Reasonable Expectation of Privacy' Test Defies Expectations

Neil Gorsuch proposes an alternative to a Fourth Amendment standard that has proven to be an unreliable safeguard against government snooping.

Jacob Sullum | 7.8.2026 12:10 PM

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When he was arrested in 1965, Charles Katz "was probably the preeminent college basketball handicapper in America." Or so says Harvey Schneider, who presumably should know, since he later represented Katz at the Supreme Court in a landmark Fourth Amendment case.

The Court's 1967 decision in Katz v. United States, which held that the Constitution's prohibition of "unreasonable searches and seizures" applies when people have a "reasonable expectation of privacy," continues to shape Fourth Amendment rulings six decades later. That was clear on June 29, when the Court decided Chatrie v. United States, holding that a government-ordered analysis of cellphone location data qualifies as a "search" under the Fourth Amendment.

"An individual has a reasonable expectation of privacy in records about his cell phone's location, and police intrude on that constitutionally protected interest when they demand the information," Justice Elena Kagan wrote in an opinion joined by four of her colleagues. Justice Neil Gorsuch agreed with the result but not the rationale. The Katz test, he complained, "has no basis in the Constitution's text or history." He added that it has proven unworkable in practice because it has never been clear how courts should determine whether an expectation of privacy is "reasonable."

Gorsuch is surely right that the Katz test has produced inconsistent and puzzling results. In cases addressing intrusions such as trash searches, demands for bank and telephone records, surveillance by low-flying aircraft, and police trespassing on private property, the Supreme Court has perceived no expectations of privacy it was prepared to recognize as reasonable. Applying the same test, it has repeatedly ruled that the Fourth Amendment does not apply to information that people voluntarily share with third parties. Yet the Court has repeatedly rebelled at the disturbing implications of that principle without explicitly renouncing it.

That is what happened in Chatrie, which involved a Virginia bank robbery investigation. Police used a "geofence" warrant to identify the perpetrator by requiring Google to search customer data collected by its Location History feature, which tracks the whereabouts of cellphone users. For reasons that are not entirely clear, the Court declined to apply the third-party doctrine, instead reverting to the original, unmodified Katz test.

A better approach, Gorsuch argued, would be to treat Location History records as "effects" covered by the Fourth Amendment—as a form of personal property, in other words. While it is not clear exactly how that property-rights approach would work in other contexts, it does seem less malleable than the Katz test, which gives courts wide discretion in discerning expectations and deciding whether they are reasonable. Gorsuch aptly likened the Court's understanding of that test to its definition of obscenity in the 1960s: "We know a 'reasonable expectation of privacy' (and an exception to the third party doctrine) when we see it."

The Roots of the 'Reasonable Expectation' Test

To understand why the object of Gorsuch's ire seemed like a good idea at the time, it helps to review the facts of Katz's case. The bookie, who had an apartment on Sunset Boulevard in Los Angeles that the Associated Press described as "expensive," would often conduct his business from one of three telephone booths near his building, which proved to be his downfall.

After FBI agents "got wind of Katz's activities and set out to arrest him," Schneider says, they devised "a rather elaborate plan to do so." First, "the agents obtained the telephone
company's consent to put one of the telephone booths out of order." Then they attached microphones to the roofs of the other two booths. The microphones, which were wired to a recorder on top of one booth, captured Katz's voice as he made calls to Boston and Miami, relaying bets on basketball games, including contests pitting Duquesne University against St. Bonaventure College and Temple against Lafayette.

Katz's phone calls violated 18 USC 1084, which made it a federal crime for someone "engaged in the business of betting or wagering" to transmit wagers on sporting events or information facilitating such bets "in interstate or foreign commerce" via a "wire communication facility." A federal judge in Los Angeles convicted Katz of eight counts and imposed a $300 fine—about $3,200 today.

On appeal, Katz argued that the evidence collected by the FBI's recorder should have been suppressed because the Fourth Amendment requires a warrant for such eavesdropping. He relied on Silverman v. United States, a 1961 Supreme Court case that also involved a gambling investigation. To verify their suspicions that a row house was "the headquarters of a gambling operation," District of Columbia police officers drove a "spike mike" into the wall of an adjoining house with the owner's permission. The microphone made contact with a heating duct in the suspects' house, enabling the cops to overhear their conversations.

"The eavesdropping was accomplished by means of an unauthorized physical penetration into the premises occupied by the petitioners," Justice Potter Stewart wrote in the majority opinion. "Eavesdropping accomplished by means of such a physical intrusion is beyond the pale of even those decisions in which a closely divided Court has held that eavesdropping accomplished by other electronic means did not amount to an invasion of Fourth Amendment rights."

One of the precedents Stewart had in mind was Olmstead v. United States, a 1928 case in which the Court concluded that wiretapping did not implicate the Fourth Amendment. Another relevant decision was the Court's 1942 ruling in Goldman v. United States, which held that federal agents did not violate the Fourth Amendment when they eavesdropped on the conversations of criminal suspects by placing a "detectaphone" against the wall of an adjoining room. Stewart saw an important difference between remote wiretapping or listening through a wall and poking a microphone into a suspect's property.

Unfortunately for Katz, the U.S. Court of Appeals for the 9th Circuit thought the FBI's eavesdropping on him more closely resembled the facts of Goldman. "There was no physical penetration inside of the booths," the 9th Circuit noted when it rejected Katz's appeal in November 1966.

A year later in Katz v. United States, the Supreme Court deemed that detail irrelevant. Writing for the majority, Stewart said "the underpinnings of Olmstead and Goldman have been so eroded by our subsequent decisions that the 'trespass' doctrine there enunciated can no longer be regarded as controlling." The main point, Stewart said, was that the FBI had "violated the privacy upon which [Katz] justifiably relied while using the telephone booth." In other words, Justice John Marshall Harlan II said in a concurring opinion, the Fourth Amendment applies when someone has an "expectation of privacy" that "society is prepared to recognize as 'reasonable.'"

'The Limits of Katz's Reach'

When it sided with Katz, the Supreme Court said the Fourth Amendment's scope "cannot turn upon the presence or absence of a physical intrusion into any given enclosure," rejecting the premise that had led the Court to approve warrantless wiretapping four decades earlier. For anyone concerned about government snooping, that was surely a good result. But subsequent decisions showed the new test was an unreliable safeguard against police invasions of privacy.

"If Katz ushered in a revolution in Fourth Amendment doctrine, the Court was quick to cabin its........

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