18 U.S.C. § 3125

(a) Notwithstanding any other provision of this chapter, any investigative or law enforcement officer, specially designated by the Attorney General, the Deputy Attorney General, the Associate Attorney General, any Assistant Attorney General, any acting Assistant Attorney General, or any Deputy Assistant Attorney General, or by the principal prosecuting attorney of any State or subdivision thereof acting pursuant to a statute of that State, who reasonably determines that— (1) an emergency situation exists that involves— (A) immediate danger of death or serious bodily injury to any person; (B) conspiratorial activities characteristic of organized crime; (C) an immediate threat to a national security interest; or (D) an ongoing attack on a protected computer (as defined in section 1030) that constitutes a crime punishable by a term of imprisonment greater than one year; that requires the installation and use of a pen register or a trap and trace device before an order authorizing such installation and use can, with due diligence, be obtained, and (2) there are grounds upon which an order could be entered under this chapter to authorize such installation and use; may have installed and use a pen register or trap and trace device if, within forty-eight hours after the installation has occurred, or begins to occur, an order approving the installation or use is issued in accordance with section 3123 of this title . (b) In the absence of an authorizing order, such use shall immediately terminate when the information sought is obtained, when the application for the order is denied or when forty-eight hours have lapsed since the installation of the pen register or trap and trace device, whichever is earlier. (c) The knowing installation or use by any investigative or law enforcement officer of a pen register or trap and trace device pursuant to subsection (a) without application for the authorizing order within forty-eight hours of the installation shall constitute a violation of this chapter. (d) A provider of a wire or electronic service, landlord, custodian, or other person who furnished facilities or technical assistance pursuant to this section shall be reasonably compensated for such reasonable expenses incurred in providing such facilities and assistance.