From the Snowden leaks to the revelations about government surveillance of United States citizens in the name of national security, privacy is in the news these days as it has not been in recent memory. The issue promises to gain more attention in April, when the U.S. Supreme Court is scheduled to hear arguments in cases addressing the question whether police need a warrant to search the contents of a cellphone found on a person who has been arrested. Given the ubiquity of cell phone ownership and use in this country, we should all have more than a passing interest in the Supreme Court’s answer to this question.

These cases—United States v. Wurie and Riley v. California—may require the justices to revisit a case it decided in 1979, Smith v. Maryland. In Smith, the court concluded that the Fourth Amendment does not require the government to secure a search warrant before obtaining the telephone numbers individuals dial from their own phones. Telephone users, the court reasoned, must know that, when they make calls, the information conveyed to the telephone company is recorded in the ordinary course of business and, accordingly, there is no reasonable expectation of privacy in that information. Smith lies at the core of the “third-party doctrine,” which holds that you have no constitutionally protectable privacy interest in information you voluntarily disclose to others.

The Smith court arguably misunderstood the import of what it means to have a reasonable expectation of privacy for constitutional purposes. The traditional test comes from Justice John Harlan’s concurrence in Katz v. United States, in which he stated that a government search implicates the Fourth Amendment’s protection of privacy only when an individual has a reasonable expectation of privacy—that is, when she has demonstrated that her subjective expectation of privacy is one that society is willing to accept as reasonable.

Often neglected is the majority opinion in Katz, by Justice Potter Stewart. The majority’s view of the facts suggests that determining whether a person has a reasonable expectation of privacy is a normative exercise, not just a descriptive one. Katz concerned FBI efforts to eavesdrop via a listening device attached to the outside of a public telephone booth. Stewart noted that the fact that the phone booth was made of glass and the defendant was visible within were immaterial to the constitutional question: “One who occupies [a phone booth], shuts the door behind him, and pays the toll that permits him to place a call is surely entitled to assume that the words he utters into the mouthpiece will not be broadcast to the world.”

To be clear, the Court was not saying that the defendant enjoyed Fourth Amendment protection because the phone booth itself perfectly secured his privacy. Indeed, someone close to the phone booth could have read the defendant’s lips and thereby learned at least his side of the conversation. Rather, the majority was noting that the defendant’s circumstances should be regarded as sufficiently private for constitutional purposes, because, as Stewart put it, “what [an individual] seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.”

The Smith court eschewed the normative component that underlies Katz and adopted instead a purely descriptive view of privacy, concluding that information revealed to the telephone company—or indeed any third party—automatically compromises an individual’s expectation of privacy. That court could scarcely have imagined the effect of this conclusion in a world in which cellular communication is ubiquitous. Today, cell phone service providers know a good deal more about their customers than the telephone company did about theirs in the late 1970s. In addition to call numbers, providers know where a cell phone user made a call, and so it may be possible, for example, to retroactively track a person’s movements using what is known as historical cell site location information (“CSLI”). In many cases, federal courts have held that individuals have no expectation of privacy in such information.

But, last month, a state court held otherwise. In Commonwealth v. Augustine, the Massachusetts Supreme Judicial Court reasoned that, given “the nature of cellular telephone technology and CSLI and the character of cell phone use in our current society,” the third-party doctrine does not apply to such information. While it did not abandon the third-party doctrine under the state constitutional equivalent of the Fourth Amendment, the Supreme Judicial Court did conclude that individuals often will have a reasonable expectation of privacy in historical CSLI, notwithstanding that the information was voluntarily supplied to the service provider when they used their cell phones. In other words, even in situations in which perfect privacy does not exist as a descriptive matter, the court recognized that information may be protected nonetheless.

Like the Massachusetts high court, some judges have suggested that the advent of digital communications technology may require the court to reconsider the extent of the third-party doctrine. Justice Sonia Sotomayor, for instance, has argued that the approach developed in Smith “is ill-suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks.”

The cases the U.S. Supreme Court is scheduled to hear in April may not provide the right opportunity for the court to revisit the premises underlying the third-party doctrine, but that case will come soon enough. There is, as Justice Sotomayor correctly observed, little communicative activity in which we engage today that does not involve some third-party assistance; just because we disclose information to individuals and entities with which we have relationships of trust—like our cell phone service provider—should not mean we have at the same time sacrificed our right not to share that information with everyone else.