Smith v. Maryland

Mr. Justice Blackmun

delivered the opinion of the Court.

This case presents the question whether the installation and use of a pen register1 constitutes a “search” within the meaning of the Fourth Amendment,2 made applicable to the States through the Fourteenth Amendment. Mapp v. Ohio, 367 U. S. 643 (1961).

*737 I

On March 5, 1976, in Baltimore, Md., Patricia McDonough was robbed. She gave the police a description of the robber and of a 1975 Monte Carlo automobile she had observed near the scene of the crime. Tr. 66-68. After the robbery, McDonough began receiving threatening and obscene phone calls from a man identifying himself as the robber. On one occasion, the caller asked that she step out on her front porch; she did so, and saw the 1975 Monte Carlo she had earlier described to police moving slowly past her home. Id., at 70. On March 16, police spotted a man who met McDonough’s description driving a 1975 Monte Carlo in her neighborhood. Id., at 71-72. By tracing the license plate number, police learned that the car was registered in the name of petitioner, Michael Lee Smith. Id., at 72.

The next day, the telephone company, at police request, installed a pen register at its central offices to record the numbers dialed from the telephone at petitioner’s home. Id., at 73, 75. The police did not get a warrant or court order before having the pen register installed. The register revealed that on March 17 a call was placed from petitioner’s home to McDonough’s phone. Id., at 74. On the basis of this and other evidence, the police obtained a warrant to search petitioner’s residence. Id., at 75. The search revealed that a page in petitioner’s phone book was turned down to the name and number of Patricia McDonough; the phone book was seized. Ibid. Petitioner was arrested, and a six-man lineup was held on March 19. McDonough identified petitioner as the man who had robbed her. Id., at 70-71.

Petitioner was indicted in the Criminal Court of Baltimore for robbery. By pretrial motion, he sought to suppress “all fruits derived from the pen register” on the ground that the police had failed to secure a warrant prior to its installation. Record 14; Tr. 54 — 56. The trial court denied the suppression motion, holding that the warrantless installation of the pen *738 register did not violate the Fourth Amendment. Id., at 63. Petitioner then waived a jury, and the case was submitted to the court on an agreed statement of facts. Id., at 65-66. The pen register tape (evidencing the fact that a phone call had been made from petitioner’s phone to McDonough’s phone) and the phone book seized in the search of petitioner’s residence were admitted into evidence against him. Id., at 74-76. Petitioner was convicted, id., at 78, and was sentenced to six years. He appealed to the Maryland Court of Special Appeals, but the Court of Appeals of Maryland issued a writ of certiorari to the intermediate court in advance of its decision in order to consider whether the pen register evidence had been properly admitted at petitioner’s trial. 283 Md. 156, 160, 389 A. 2d 858, 860 (1978).

The Court of Appeals affirmed the judgment of conviction, holding that “there is no constitutionally protected reasonable expectation of privacy in the numbers dialed into a telephone system and hence no search within the fourth amendment is implicated by the use of a pen register installed at the central offices of the telephone company.” Id., at 173, 389 A. 2d, at 867. Because there was no “search,” the court concluded, no warrant was needed. Three judges dissented, expressing the view that individuals do have a legitimate expectation of privacy regarding the phone numbers they dial from their homes; that the installation of a pen register thus constitutes a “search”; and that, in the absence of exigent circumstances, the failure of police to secure a warrant mandated that the pen register evidence here be excluded. Id., at 174, 178, 389 A. 2d, at 868, 870. Certiorari was granted in order to resolve indications of conflict in the decided cases as to the restrictions imposed by the Fourth Amendment on the use of pen registers.3 439 U. S. 1001 (1978).

*739 II

A

The Fourth Amendment guarantees “'[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.” In determining whether a particular form of government-initiated electronic surveillance is a “search” within the meaning of the Fourth Amendment,4 our lodestar is Katz v. United States, 389 U. S. 347 (1967). In Katz, Government agents had intercepted the contents of a telephone conversation by attaching an electronic listening device to the outside of a public phone booth. The Court rejected the argument that a “search” can occur only when there has been a “physical intrusion” into a “constitutionally protected area,” noting that the Fourth Amendment “protects people, not places.” Id., at 351-353. Because the Government’s monitoring of Katz’ conversation “violated the privacy upon which he justifiably relied while using the telephone booth,” the Court held that *740 it “constituted a 'search and seizure’ within the meaning of the Fourth Amendment.” Id., at 353.

Consistently with Katz, this Court uniformly has held that the application of the Fourth Amendment depends on whether the person invoking its protection can claim a “justifiable,” a “reasonable,” or a “legitimate expectation of privacy” that has been invaded by government action. E. g., Rakas v. Illinois, 439 U. S. 128, 143, and n. 12 (1978); id., at 150, 151 (concurring opinion); id., at 164 (dissenting opinion) ; United States v. Chadwick, 433 U. S. 1, 7 (1977); United States v. Miller, 425 U. S. 435, 442 (1976); United States v. Dionisio, 410 U. S. 1, 14 (1973); Couch v. United States, 409 U. S. 322, 335-336 (1973); United States v. White, 401 U. S. 745, 752 (1971) (plurality opinion); Mancusi v. DeForte, 392 U. S. 364, 368 (1968); Terry v. Ohio, 392 U. S. 1, 9 (1968). This inquiry, as Mr. Justice Harlan aptly noted in his Katz concurrence, normally embraces two discrete questions. The first is whether the individual, by his conduct, has “exhibited an actual (subjective) expectation of privacy,” 389 U. S., at 361 — whether, in the words of the Katz majority, the individual has shown that “he seeks to preserve [something] as private.” Id., at 351. The second question is whether the individual’s subjective expectation of privacy is “one that society is prepared to recognize as 'reasonable,’ ” id., at 361— whether, in the words of the Katz majority, the individual’s expectation, viewed objectively, is “justifiable” under the circumstances. Id., at 353.5 See Rakas v. Illinois, 439 U. S., *741 at 143-144, n. 12; id., at 151 (concurring opinion); United States v. White, 401 U. S., at 752 (plurality opinion).

B

In applying the Katz analysis to this case, it is important to begin by specifying precisely the nature of the state activity that is challenged. The activity here took the form of installing and using a pen register. Since the pen register was installed on telephone company property at the telephone company’s central offices, petitioner obviously cannot claim that his “property”’ was invaded or that police intruded into a “constitutionally protected area.” Petitioner’s claim, rather, is that, notwithstanding the absence of a trespass, the State, as did the Government in Katz, infringed a “legitimate expectation of privacy” that petitioner held. Yet a pen register differs significantly from the listening device employed in Katz, for pen registers do not acquire the contents of communications. This Court recently noted:

“Indeed, a law enforcement official could not even determine from the use of a pen register whether a communication existed. These devices do not hear sound. They disclose only the telephone numbers that have been dialed — a means of establishing communication. Neither the purport of any communication between the caller and the recipient of the call, their identities, nor whether the call was even completed is disclosed by pen registers.” United States v. New York Tel. Co., 434 U. S. 159, 167 (1977).

*742 Given a pen register’s limited capabilities, therefore, petitioner’s argument that its installation and use constituted a “search” necessarily rests upon a claim that he had a “legitimate expectation of privacy” regarding the numbers he dialed on his phone.

This claim must be rejected. First, we doubt that people in general entertain any actual expectation of privacy in the numbers they dial. All telephone users realize that they must “convey” phone numbers to the telephone company, since it is through telephone company switching equipment that their calls are completed. All subscribers realize, moreover, that the phone company has facilities for making permanent records of the numbers they dial, for they see a list of their long-distance (toll) calls on their monthly bills. In fact, pen registers and similar devices are routinely used by telephone companies “for the purposes of checking billing operations, detecting fraud, and preventing violations of law.” United States v. New York Tel. Co., 434 U. S., at 174-175. Electronic equipment is used not only to keep billing records of toll calls, but also “to keep a record of all calls dialed from a telephone which is subject to a special rate structure.” Hodge v. Mountain States Tel. & Tel. Co., 555 F. 2d 254, 266 (CA9 1977) (concurring opinion). Pen registers are regularly employed “to determine whether a home phone is being used to conduct a business, to check for a defective dial, or to check for overbilling.” Note, The Legal Constraints upon the Use of the Pen Register as a Law Enforcement Tool, 60 Cornell L. Rev. 1028, 1029 (1975) (footnotes omitted). Although most people may be oblivious to a pen register’s esoteric functions, they presumably have some awareness of one common use: to aid in the identification of persons making annoying or obscene calls. See, e. g., Von Lusch v. C & P Telephone Co., 457 F. Supp. 814, 816 (Md. 1978); Note, 60 Cornell L. Rev., at 1029-1030, n. 11; Claerhout, The Pen Register, 20 Drake L. Rev. 108, 110-111 (1970). Most phone books tell *743 subscribers, on a page entitled “Consumer Information/’ that the company “can frequently help in identifying to the authorities the origin of unwelcome and troublesome calls.” E. g., Baltimore Telephone Directory 21 (1978); District of Columbia Telephone Directory 13 (1978). Telephone users, in sum, typically know that they must convey numerical information to the phone company; that the phone company has facilities for recording this information; and that the phone company does in fact record this information for a variety of legitimate business purposes. Although subjective expectations cannot be scientifically gauged, it is too much to believe that telephone subscribers, under these circumstances, harbor any general expectation that the numbers they dial will remain secret.

Petitioner argues, however, that, whatever the expectations of telephone users in general, he demonstrated an expectation of privacy by his own conduct here, since he “us'[ed] the telephone in his house to the exclusion of all others.” Brief for Petitioner 6 (emphasis added). But the site of the call is immaterial for purposes of analysis in this case. Although petitioner’s conduct may have been calculated to keep the contents of his conversation private, his conduct was not and could not have been calculated to preserve the privacy of the number he dialed. Regardless of his location, petitioner had to convey that number to the telephone company in precisely the same way if he wished to complete his call. The fact that he dialed the number on his home phone rather than on some other phone could make no conceivable difference, nor could any subscriber rationally think that it would.

Second, even if petitioner did harbor some subjective expectation that the phone numbers he dialed would remain private, this expectation is not “one that society is prepared to recognize as 'reasonable.’ ” Katz v. United States, 389 U. S., at 361. This Court consistently has held that a person has no legitimate expectation of privacy in information he *744 voluntarily turns over to third parties. E. g., United States v. Miller, 425 U. S., at 442-444; Couch v. United States, 409 U. S., at 335-336; United States v. White, 401 U. S., at 752 (plurality opinion); Hoffa v. United States, 385 U. S. 293, 302 (1966); Lopez v. United States, 373 U. S. 427 (1963). In Miller, for example, the Court held that a bank depositor has no “legitimate 'expectation of privacy’ ” in financial information “voluntarily conveyed to . . . banks and exposed to their employees in the ordinary course of business.” 425 U. S., at 442. The Court explained:

“The depositor takes the risk, in revealing his affairs to another, that the information will be conveyed by that person to the Government. . . . This Court has held repeatedly that the Fourth Amendment does not prohibit the obtaining of information revealed to a third party and conveyed by him to Government authorities, even if the information is revealed on the assumption that it will be used only for a limited purpose and the confidence placed in the third party will not be betrayed.” Id., at 443.

Because the depositor “assumed the risk” of disclosure, the Court held that it would be unreasonable for him to expect his financial records to remain private.

This analysis dictates that petitioner can claim no legitimate expectation of privacy here. When he used his phone, petitioner voluntarily conveyed numerical information to the telephone company and “exposed” that information to its equipment in the ordinary course of business. In so doing, petitioner assumed the risk that the company would reveal to police the numbers he dialed. The switching equipment that processed those numbers is merely the modern counterpart of the operator who, in an earlier day, personally completed calls for the subscriber. Petitioner concedes that if he had placed his calls through an operator, he could claim no legitimate expectation of privacy. Tr. of Oral Arg. 3-5, 11-12, 32. We *745 are not inclined to hold that a different constitutional result is required because the telephone company has decided to automate.

Petitioner argues, however, that automatic switching equipment differs from a live operator in one pertinent respect. An operator, in theory at least, is capable of remembering every number that is conveyed to him by callers. Electronic equipment, by contrast, can “remember” only those numbers it is programmed to record, and telephone companies, in view of their present billing practices, usually do not record local calls. Since petitioner, in calling McDonough, was making a local call, his expectation of privacy as to her number, on this theory, would be “legitimate.”

This argument does not withstand scrutiny. The fortuity of whether or not the phone company in fact elects to make a quasi-permanent record of a particular number dialed does not, in our view, make any constitutional difference. Regardless of the phone company’s election, petitioner voluntarily conveyed to it information that it had facilities for recording and that it was free to record. In these circumstances, petitioner assumed the risk that the information would be divulged to police. Under petitioner’s theory, Fourth Amendment protection would exist, or not, depending on how the telephone company chose to define local-dialing zones, and depending on how it chose to bill its customers for local calls. Calls placed across town, or dialed directly, would be protected; calls placed across the river, or dialed with operator assistance, might not be. We are not inclined to make a crazy quilt of the Fourth Amendment, especially in circumstances where (as here) the pattern of protection would be dictated by billing practices of a private corporation.

We therefore conclude that petitioner in all probability entertained no actual expectation of privacy in the phone numbers he dialed, and that, even if he did, his expectation was not “legitimate.” The installation and use of a pen reg *746 ister, consequently, was not a “search,” and no warrant was required. The judgment of the Maryland Court of Appeals is affirmed.

It is so ordered.

Mr. Justice Powell took no part in the consideration or decision of this case.

“A pen register is a mechanical device that records the numbers dialed on a telephone by monitoring the electrical impulses caused when the dial on the telephone is released. It does not overhear oral communications and does not indicate whether calls are actually completed.” United States v. New York Tel. Co., 434 U. S. 159, 161 n. 1 (1977). A pen register is “usually installed at a central telephone facility [and] records on a paper tape all numbers dialed from [the] line” to which it is attached. United States v. Giordano, 416 U. S. 505, 549 n. 1 (1974) (opinion concurring in part and dissenting in part). See also United States v. New York Tel. Co., 434 U. S., at 162.

“The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.” U. S. Const., Arndt. 4.

See Application of United States for Order, 546 F. 2d 243, 245 (CA8 1976), cert. denied sub nom. Southwestern Bell Tel. Co. v. United States, 434 U. S. 1008 (1978); Application of United States in Matter of Order, *739 538 F. 2d 956, 959-960 (CA2 1976), rev’d on other grounds sub nom. United States v. New York Tel. Co., 434 U. S. 159 (1977); United States v. Falcone, 505 F. 2d 478, 482, and n. 21 (CA3 1974), cert. denied, 420 U. S. 955 (1975); Hodge v. Mountain States Tel. & Tel. Co., 555 F. 2d 254, 256 (CA9 1977); id., at 266 (concurring opinion); and United States v. Clegg, 509 F. 2d 605, 610 (CA5 1975). In previous decisions, this Court has not found it necessary to consider whether “pen register surveillance [is] subject to the requirements of the Fourth Amendment.” United States v. New York Tel. Co., 434 U. S., at 165 n. 7. See United States v. Giordano, 416 U. S., at 554 n. 4 (opinion concurring in part and dissenting in part).

In this case, the pen register was installed, and the numbers dialed were recorded, by the telephone company. Tr. 73-74. The telephone company, however, acted at police request. Id., at 73, 75. In view of this, respondent appears to concede that the company is to be deemed an “agent” of the police for purposes of this case, so as to render the installation and use of the pen register “state action” under the Fourth and Fourteenth Amendments. We may assume that “state action” was present here.

Situations can be imagined, of course, in which Katz’ two-pronged inquiry would provide an inadequate index of Fourth Amendment protection. For example, if the Government were suddenly to announce on nationwide television that all homes henceforth would be subject to war-rantless entry, individuals thereafter might not in fact entertain any actual expectation of privacy regarding their homes, papers, and effects. Similarly, if a refugee from a totalitarian country, unaware of this Nation’s traditions, erroneously assumed that police were continuously monitoring his telephone conversations, a subjective expectation of privacy regarding *741 the contents of his calls might be lacking as well. In such circumstances, where an individual’s subjective expectations had been “conditioned” by influences alien to well-recognized Fourth Amendment freedoms, those subjective expectations obviously could play no meaningful role in ascertaining what the scope of Fourth Amendment protection was. In determining whether a “legitimate expectation of privacy” existed in such cases, a normative inquiry would be proper.