The victim of a robbery began receiving phone calls from the person who claimed to be the robber. After developing a suspect, the government installed a pen register, without a warrant, at the central telephone system to determine the specific phone numbers the suspect was dialing. After the government discovered the suspect had called the victim, the suspect (defendant) was charged him with robbery.
Whether the use of the pen register constituted a search?
No. The defendant did not have a reasonable expectation of privacy in the phone numbers he dialed.
The Court found that the defendant did not have a reasonable expectation of privacy regarding the numbers he dialed on his phone since those numbers were automatically turned over to a third party, the phone company. Even if the defendant did harbor some subjective expectation that the phone numbers he dialed would remain private, this expectation was not one that society was prepared to recognize as “reasonable.” Therefore, the Court concluded that installation of the pen register was not a “search” and no warrant was required.
442 U.S. 735, 99 S. Ct. 2577 (1979)