The Katz Privacy Test

The Katz Privacy Test

The modern definition of a Fourth Amendment "search" comes from Katz v. United States. The Court held there that electronic surveillance intruding on a person's reasonable expectation of privacy is a search and generally requires a warrant.¹ The same decision marks the limit of that rule: conversations exposed to the public, and conversations for which no effort is made to preserve privacy, receive no Fourth Amendment protection.² "Search" is therefore a term of art, a word whose legal meaning departs from everyday usage. Sifting through a suspect's garbage or watching a yard from an airplane would be called searching in ordinary speech, yet neither is a search under the Amendment.³ Because the definition decides whether the Amendment applies at all, it is the first gate of the analysis described above.

The Court moved to a privacy-based definition because a definition built on physical intrusion leaves a gap. For most of its history the Amendment was read as guarding against government trespass on the persons, houses, papers, and effects it lists.⁴ Surveillance, however, can see and hear without crossing a threshold or touching anything. If trespass alone defined a search, the government could escape the Amendment simply by choosing a technique that never penetrates an enclosure, however much of a person's private life it exposed. Katz closes that gap by asking what the person was entitled to expect. In the Court's phrasing, the Amendment protects people, not places: what a person knowingly exposes to the public is unprotected even in his own home or office, but what he seeks to preserve as private may be protected even in an area open to the public.⁵

Justice Harlan's concurrence supplied the wording that courts apply. It asks, first, whether the person has exhibited an actual (subjective) expectation of privacy and, second, whether that expectation is one that society is prepared to recognize as "reasonable."⁶ Each half does separate work. A test that looked only to the person's own expectation would let anyone claim protection anywhere by saying they expected privacy, including in settings where society would never honor the claim. A test that looked only to what society finds reasonable would hand judges the task of deciding what privacy people ought to want, and it would protect a person who never tried to keep anything private. Requiring both makes the individual show actual effort to preserve privacy and requires that society be prepared to honor the claim.

The privacy route is one of two ways into the Amendment. In United States v. Jones the majority found a search because the government physically occupied private property to obtain information, and it left the privacy question aside.⁷ That trespass route supplements Katz rather than replacing it, so government conduct is a search if it satisfies either test.⁸ Both routes also presuppose government conduct. When a private freight carrier opened a package and police later found nothing more than the carrier had, there was no search. Searches by private employers are usually challenged under state tort law instead.⁹ Public school administrators and a deputy sheriff who demanded a student's Facebook credentials, by contrast, were government actors, and the court treated the student's private messages like letters in denying dismissal of her Fourth Amendment claim in the Minnewaska school-district litigation.¹⁰ The sections that follow take the privacy route in order: the move from trespass to privacy, the person's subjective expectation, and then society's recognition of that expectation as reasonable.

From Trespass to Privacy

The case that moved the definition of a search away from physical intrusion began as an ordinary gambling prosecution. In Katz v. United States, FBI agents attached an electronic listening and recording device to the outside of a public telephone booth and recorded the petitioner's end of calls in which he passed wagering information from Los Angeles to Miami and Boston.¹² The government offered those recordings at trial over his objection, and the court of appeals affirmed the conviction because the agents had never physically entered the space he occupied.¹³ That reasoning tracked a long-standing assumption that the Amendment reached only tangible property, so that a technique which did not penetrate an enclosure fell outside it.¹⁴ The older wiretap decision in Olmstead v. United States shows how the assumption worked. It treated telephone wires running out of a house as no part of the house, which meant that tapping them entered nothing the Amendment protected.¹⁵

Both sides in Katz argued the case in the vocabulary of place. The petitioner contended that the booth was a constitutionally protected area, and the government answered that it was not and that physical penetration was required in any event.¹⁶ The Court declined to adopt that formulation, reasoning that asking in the abstract whether a given area is protected deflects attention from the real problem.¹⁷ Its replacement is the people, not places principle: the Fourth Amendment protects people, and what matters is what a person has done to keep something private.¹⁸ The principle has two halves. What a person knowingly exposes to the public, even in his own home or office, receives no protection, while what he seeks to preserve as private, even in an area accessible to the public, may be protected.¹⁹ The second half is what gave Katz a claim. He did not own the booth and was one caller among many using a facility open to everyone, so a test built on who controls the place would have left him with nothing, while a test built on what he sought to keep private did not.²⁰

The government's best factual point was that the booth was partly glass, so the caller was as visible inside as he would have been standing on the sidewalk.²¹ The Court's answer shows how the privacy inquiry actually works. What Katz wanted to keep out was the "uninvited ear," and the visibility of his body through the glass did not cost him the right to exclude a listener.²² Privacy is therefore selective: a person may leave one channel open to the world while closing another. By shutting the door behind him and paying the toll, a caller is entitled to assume that the words he speaks into the mouthpiece will not be broadcast to the world.²³ Those two acts of closing the door and paying for the call are the kind of conduct the next section treats as evidence of an actual expectation of privacy.

Having characterized the booth, the Court met the government's main argument, that without physical penetration there was no search. It rejected the premise that property interests control the government's power to search and seize, and it held that the Amendment's reach cannot depend on whether an enclosure was physically entered, so that the device's failure to pierce the booth wall had no constitutional significance.²⁴ The reason lies in how surveillance works. Technology lets police see and hear a person's activities and conversations without being anywhere near them, so a rule requiring penetration of walls would catch the clumsy intrusions and miss the unobtrusive ones.²⁵ Under a trespass-only definition, the government could avoid the Amendment altogether by mounting its device on the outside of the wall, and protection would then depend on where the technician happened to attach the equipment instead of on how much of a person's private life was exposed. Students lose this issue when they treat the absence of a physical entry as the end of the analysis.

Two limits keep the holding from being read too broadly. The Court stated that the Fourth Amendment cannot be translated into a general constitutional right to privacy: it protects individual privacy against certain kinds of governmental intrusion, and a person's broader right to be let alone is left largely to state law.²⁶ Other decisions treat the Fourth Amendment as one source among several of wider zones of privacy,²⁷ but within Fourth Amendment doctrine the question remains whether government conduct intruded on a protected interest. The second limit is that Katz did not retire property-based protection. It decided that physical penetration is unnecessary for a search, not that physical intrusion no longer counts, and the Court later made clear that Katz supplements the older physical-intrusion route instead of displacing it.²⁸ That surviving route is the subject of the section on physical intrusion and the home. Finally, calling the recording a search answers only the first gate described in the introduction. Whether the agents' care in limiting the surveillance made it reasonable is a separate question that arises only after both gates are passed.²⁹

see above

Society's Recognition of Privacy

The first prong of the privacy test looks at the person's own conduct, and the second looks outward. Justice Harlan's formulation in Katz v. United States requires that the expectation the person exhibited also be one that society is prepared to recognize as "reasonable."³¹ Justice Powell, concurring in Rakas v. Illinois, stated the consequence plainly: it is not enough that an individual desired or anticipated freedom from government intrusion, because only legitimate expectations of privacy are protected.³² The reason is structural. A person with something to hide has the strongest wish that no one find it, so a test that rewarded wishes would give the most protection to the most determined concealment, and the reach of the Amendment would shift from one person to the next with no way for an officer to know the limit in advance. Measuring the expectation against shared social understanding gives officers and courts a common reference point, although, as Justice Powell acknowledged, the standard offers no bright line between the protected and the unprotected.³³

The Court measures reasonableness against the Amendment's purposes. In California v. Ciraolo the Court restated the test of legitimacy as whether the government's intrusion infringes "the personal and societal values protected by the Fourth Amendment," and it added that the test does not ask whether the individual chose to conceal assertedly private activity.³⁴ That framing moves attention from the person's effort to the kind of intrusion and the kind of interest at stake. A fence, a locked door, or a covered window can establish the first prong, yet none of them settles the second. Students lose this issue when they treat a sincere effort at concealment as proof that society will recognize the expectation.

Because legitimacy turns on those values, the Court weighs several considerations, and no single one is dispositive.³⁵ The decisions have given weight to these:

• the intention of the Framers of the Fourth Amendment;
• the uses to which the individual has put the location; and
• the societal understanding that certain areas deserve the most scrupulous protection from government invasion.

These considerations converge on the home. The Court's decisions treat a home as a place in which a subjective expectation of privacy virtually always will be legitimate, because the core of the Amendment is the right to retreat into one's own home and be free there from unreasonable government intrusion.³⁶ The curtilage, the area immediately surrounding the house and associated with it, is treated as part of the home for this purpose, so a fenced backyard can carry the same presumption.³⁷ That emphasis on place can look inconsistent with the principle that the Amendment protects people and not places, but the two fit together. The Court has recognized that the second prong often must be decided by reference to a place, since a place tells a court what society has long understood about privacy there.³⁸ The presumption for the home is strong but has limits, as the contrast below shows.

The phone booth and the fenced backyard show how the second prong can separate two people who both passed the first. In Katz the caller shut the door and paid for the call, and society is prepared to recognize the expectation that the conversation would not be intercepted, so the recording was a search.³⁹ In Ciraolo the homeowner enclosed the yard with high fences, and the Court accepted that the yard was within the curtilage and treated the first prong as met, since the State had not challenged the finding that the homeowner held a subjective expectation; yet it found the expectation unreasonable against officers who looked from an aircraft lawfully in navigable airspace.⁴⁰ Each had taken precautions, and the Ciraolo homeowner even had the curtilage on his side. What differs is the intrusion measured against the expectation: electronic interception of spoken words in Katz, and a naked-eye view from a public vantage point in Ciraolo. The Court explained that curtilage status does not by itself bar all police observation, since the Amendment has never required officers to shield their eyes when passing a home on public thoroughfares.⁴¹ The details of that holding belong to the later section on exposure to the public; the point here is that an expectation recognized in one setting can fail the second prong in another.

Society may also withhold recognition when a competing need outweighs the person's interest. In Hudson v. Palmer a prisoner claimed that his cell was searched and his property destroyed only to harass him, and the Court held that no search had occurred at all, because society is not prepared to recognize an expectation of privacy in a cell when officials need unrestricted access to find weapons and drugs, uncover escape plans, and keep cells sanitary.⁴² Because that threshold was never met, the alleged motive of harassment did not enter the analysis. Probationers and parolees fall between the prisoner and the ordinary citizen: in United States v. Knights the probation conditions, of which the probationer had been clearly informed, significantly reduced the reasonable expectation of privacy in the residence, and in Samson v. California the Court found parolees to have even fewer expectations of privacy.⁴³

A further way an expectation fails the second prong is wrongful presence. In Rakas the Court observed that a burglar working in a summer cabin during the off season may hold a thoroughly justified subjective expectation of not being discovered, yet the law does not call that expectation legitimate, because the burglar's presence is wrongful and society is not prepared to treat the expectation as reasonable.⁴⁴ The example shows that a legitimate expectation requires more than a subjective hope of escaping detection, and the idea returns when this chapter reaches the rules on who may challenge a search. Taken together, these applications also explain why the privacy test leaves a wide range of government activities that most people would call searches outside the Amendment.⁴⁵ One major group is what a person knowingly exposes to the public, which this chapter reaches after the property-based route that survives beside Katz.