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Case Basics
Docket No. 
Michael Lee Smith
(for the petitioner)
(Attorney General of Maryland, for the respondent)
Facts of the Case 

On March 5, 1976, Patricia McDonough was robbed in Baltimore, Maryland. She was able to give the police a description of the robber and the 1975 Monte Carlo she thought the robber was driving. Within a few days, she began receiving threatening phone calls that culminated in the caller telling her to stand on her porch, from where she observed the same Monte Carlo drive past. On March 16, the police observed the car in McDonough’s neighborhood. By running a search on the license plate number, the police learned the car was registered to Michael Lee Smith. The police contacted the telephone company and requested that a pen register, a device that only records numbers dialed, record the numbers dialed from the telephone at Smith’s home. On March 17, the pen register recorded a call from Smith’s phone to McDonough’s home, so the police obtained a warrant to search Smith’s house. During the search, police discovered a phone book with the corner turned down on the page on which McDonough’s name was found. Smith was arrested and placed in a line-up where McDonough identified him as the man who robbed her.

In pretrial, Smith filed a motion to suppress the information derived from the installation of the pen register because it was obtained without a warrant. The trial court denied the motion, Smith waived a jury, and the case was submitted to the court with an agreed-upon statement of facts. The court convicted Smith and sentenced him to six years in prison. Smith appealed to the Maryland Court of Special Appeals, but the Maryland Court of Appeals intervened by issuing a writ of certiorari. That court affirmed the conviction and held that there was no expectation of privacy to cover the numbers dialed into a telephone system, so there was no Fourth Amendment violation of the warrant requirement.


Does the installation and use of a pen register constitute a search under the Fourth Amendment?

Decision: 5 votes for Maryland, 3 vote(s) against
Legal provision: Amendment 4: Fourth Amendment

No. Justice Harry A. Blackmun delivered the opinion for the 5-3 majority. The Court held that Fourth Amendment protections are only relevant if the individual believes that the government has infringed on the individual’s reasonable expectation of privacy. This reasonable expectation of privacy does not apply to the numbers recorded by a pen register because those numbers are used in the regular conduct of the phone company’s business, a fact of which individuals are aware. Because the Fourth Amendment does not apply to information that is voluntarily given to third parties, the telephone numbers that are regularly and voluntarily provided to telephone companies by their customers do not gain Fourth Amendment protections.

Justice Potter Stewart wrote a dissent in which he argued that a person who uses a telephone has a reasonable expectation of privacy regarding the content of call. Because the telephone numbers dialed also contain information relating to the content of the call, that information is also protected by the Fourth Amendment. Justice William J. Brennan, Jr. joined in the dissent. In his separate dissent, Justice Thurgood Marshall argued that the majority opinion’s analysis depends on an individual’s choice to voluntarily turn over information, but that choice is not valid if no practical alternative exists. He wrote that no citizen should be forced to accept government monitoring of the phone numbers he dials simply by registering a phone with a telephone company. Such government intrusion on telephone records could impede the exercise of free speech or political affiliation. Therefore phone records should be subject to the Fourth Amendment’s protections. Justice Brennan also joined in the dissent.

Justice Lewis F. Powell, Jr. did not participate in the discussion or decision of this case.

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SMITH v. MARYLAND. The Oyez Project at IIT Chicago-Kent College of Law. 04 September 2015. <>.
SMITH v. MARYLAND, The Oyez Project at IIT Chicago-Kent College of Law, (last visited September 4, 2015).
"SMITH v. MARYLAND," The Oyez Project at IIT Chicago-Kent College of Law, accessed September 4, 2015,