Smith v. Maryland

Facts

On March 5, 197, 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. After the robbery, McDonough began receiving threatening and obscene phone calls from a man identifying himself as the robber. On one occasion, the police spotted a man who met McDonough’s description driving a 1975 Monte Carlo in her neighborhood. By tracing the license plate number, police learned that the car was registered to the defendant

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 defendant’s home. 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 defendant’s home to McDonough’s phone.

The defendant was charged with the robbery. He sought to exclude all evidence derived from the pen register on the ground that the police had failed to secure a warrant prior to its installation. The trial court denied the suppression motion, holding that the warrantless installation of the pen register did not violate the Fourth Amendment. The Court of Appeals reversed.