18 U.S.C. § 3121: General prohibition on pen register and trap and trace device use; exception

Except as provided in this section, no person may install or use a pen register or a trap and trace device without first obtaining a court order under section 3123 of this title or under the Foreign Intelligence Surveillance Act of 1978 ( 50 U.S.C. 1801 et seq.) or an order from a foreign government that is subject to an executive agreement that the Attorney General has determined and certified to Congress satisfies section 2523. relating to the operation, maintenance, and testing of a wire or electronic communication service or to the protection of the rights or property of such provider, or to the protection of users of that service from abuse of service or unlawful use of service; or to record the fact that a wire or electronic communication was initiated or completed in order to protect such provider, another provider furnishing service toward the completion of the wire communication, or a user of that service, from fraudulent, unlawful or abusive use of service; or (3) where the consent of the user of that service has been obtained. A government agency authorized to install and use a pen register or trap and trace device under this chapter or under State law shall use technology reasonably available to it that restricts the recording or decoding of electronic or other impulses to the dialing, routing, addressing, and signaling information utilized in the processing and transmitting of wire or electronic communications so as not to include the contents of any wire or electronic communications. Whoever knowingly violates subsection (a) shall be fined under this title or imprisoned not more than one year, or both. Except as provided in subsection (b), this title and the amendments made by this title [enacting this chapter and section 1367 of this title ] shall take effect ninety days after the date of the enactment of this Act [ Oct. 21, 1986 ] and shall, in the case of conduct pursuant to a court order or extension, apply only with respect to court orders or extensions made after this title takes effect. the day before the date of the taking effect of changes in State law required in order to make orders or installations under Federal law as amended by this title; or the date two years after the date of the enactment of this Act [ Oct. 21, 1986 ].”