the largest telephone carriers in the United States: AT&T, Verizon, and BellSouth. All three companies were paid to provide the information to the NSA. It is speculated that the database contains over 1.9 trillion call-detail records of phone calls made after September 11, 2001. The database's existence prompted fierce objection from those who viewed it as a warrantless or illegal search – nevertheless, the collection of such third-party information has been authorized by the USA PATRIOT Act, and has been upheld by the courts. US Foreign Intelligence Surveillance Court of Review In a 2002 opinion entitled In re: Sealed Case No. 02-001, the United States Foreign Intelligence Surveillance Court of Review examined all the significant appellate decisions. The court noted all the Federal courts of appeal having looked at the issue had concluded that there was such constitutional power. Furthermore, if there was such power, "FISA could not encroach on the president's constitutional power", However, In Re Sealed Case "[took] for granted" that these cases are correct: The "balancing test drawn from Keith" is a reference to United States v. U.S. District Court, in which the Supreme Court of the United States established a legal test to determine whether the primary use of the warrantless search was to collect foreign intelligence, as per presidential authority, or whether that primary use is to gather evidence for use in a criminal trial. Exceptions to the search warrant requirement The warrant requirement of the Fourth Amendment is not absolute, and a number of exceptions to that requirement have been recognized by the courts, based upon such factors as whether it is reasonable under the circumstances for officers to obtain a warrant, and whether evidence might be lost or destroyed before a warrant can be obtained. Common exceptions include: Administrative searches: Routine administrative searches; Border search: The person or property of a person is searched when they attempt to enter the United States from a foreign nation or territory; Consent: The person who is searched, or who is in control of property that is searched, agrees to the search; Exigent circumstances: A pressing need to act without delay; Inventory search: A search is conducted of items taken into police custody pursuant to a formal policy; Plain feel: Contraband or evidence of criminal activity can be recognized through a suspect's clothing during a lawful pat down; Plain view: Evidence of criminal activity can be observed