Smith v. Maryland, 442 U.S. 735 (1979)
The installation and use of a pen register, which is an electronic device that records all numbers called from a particular telephone line, by police does not constitute a violation of the "legitimate expectation of privacy" under the Fourth Amendment of the U.S. Constitution because the numbers would be available to and recorded by the phone company anyway.
U.S. Supreme CourtSmith v. Maryland, 442 U.S. 735 (1979)
Smith v. Maryland
Argued March 28, 1979
Decided June 20, 1979
442 U.S. 735
The telephone company, at police request, installed at its central offices a pen register to record the numbers dialed from the telephone at petitioner's home. Prior to his robbery trial, petitioner moved to suppress "all fruits derived from" the pen register. The Maryland trial court denied this motion, holding that the warrantless installation of the pen register did not violate the Fourth Amendment. Petitioner was convicted, and the Maryland Court of Appeals affirmed.
Held: The installation and use of the pen register was not a "search" within the meaning of the Fourth Amendment, and hence no warrant was required. Pp. 442 U. S. 739-746.
(a) Application of the Fourth Amendment depends on whether the person invoking its protection can claim a "legitimate expectation of privacy" that has been invaded by government action. This inquiry normally embraces two questions: first, whether the individual has exhibited an actual (subjective) expectation of privacy; and second, whether his expectation is one that society is prepared to recognize as "reasonable." Katz v. United States, 389 U. S. 347. Pp. 442 U. S. 739-741.
(b) Petitioner in all probability entertained no actual expectation of privacy in the phone numbers he dialed, and even if he did, his expectation was not "legitimate." First, it is doubtful that telephone users in general have any expectation of privacy regarding the numbers they dial, since they typically know that they must convey phone numbers to the telephone company and that the company has facilities for recording this information and does, in fact, record it for various legitimate business purposes. And petitioner did not demonstrate an expectation of privacy merely by using his home phone, rather than some other phone, since his conduct, although perhaps calculated to keep the contents of his conversation private, was not calculated to preserve the privacy of the number he dialed. Second, even if petitioner did harbor some subjective expectation of privacy, this expectation was not one that society is prepared to recognize as "reasonable." When petitioner voluntarily conveyed numerical information to the phone company and "exposed" that information to its equipment in the normal course of business, he assumed the risk that the company would reveal the information
to the police, cf. United States v. Miller, 425 U. S. 435. Pp. 442 U. S. 741-746.
283 Md. 156, 389 A.2d 858, affirmed.
BLACKMUN, J., delivered the opinion of the Court, in which BURGER, C.J., and WHITE, REHNQUIST, and STEVENS, JJ., joined. STEWART, J., post, p. 442 U. S. 746, and MARSHALL, J., post, p. 442 U. S. 748, filed dissenting opinions, in which BRENNAN, J., joined. POWELL, J., took no part in the consideration or decision of the case.