April 2001-June 2013, EPIC: DOJ: The Attorney General's Reports on the Use of Pen Registers and Trap and Trace Devices Under the Foreign Intelligence Surveillance Act (PDF)
MARCH 3, 2014
Documents Released on U.S. Wiretapping Since Sept. 11 Terrorist Attacks
By CHARLIE SAVAGE
WASHINGTON -- Orders granted by the Foreign Intelligence Surveillance Court to allow the use of devices to secretly log the communications of suspected spies and terrorists underwent explosive growth after the Sept. 11 terrorist attacks, but leveled off and began dropping around the middle of the last decade, newly disclosed documents show.
The documents are semiannual reports to Congress from the Justice Department  showing how often it obtained orders from the surveillance court for "pen registers and trap-and-trace" devices. They keep track of metadata about incoming and outgoing phone calls and emails, showing who was involved in a conversation and when it took place, but not the contents of the communication.
The reports had been classified and have never been made public. They were obtained by the Electronic Privacy Information Center, a civil liberties and technology advocacy group, via a Freedom of Information Act lawsuit. 
The reports show a steady escalation for several years after the terrorist attacks. There were only two such orders in the first half of 2001. By that time in 2002, there were 29, and the numbers kept climbing until they peaked at 184 in the second half of 2004.
The numbers then bounced around below that level but gradually declined. They dropped to 58 in the second half of 2008 and have not been in the triple digits since. In the second half of 2012, the last period for which they were available, there were 69 such orders.
As a measure of investigative activity by year, that pattern roughly corresponds with the total number of wiretap orders issued by the Foreign Intelligence Surveillance Court each year,  according to data also compiled by the Electronic Privacy and Information Center. Such orders surged from 932 in 2001 to a peak of 2,371 in 2007, but dropped off after that.
It is not clear how the number of either pen register or wiretap orders relate to the National Security Agency's once-secret programs that collect bulk data about domestic communications and allow wiretapping without warrants if the target is a noncitizen abroad.
The administration of George W. Bush began those programs outside of the Foreign Intelligence Surveillance Act framework in 2001. But the court began authorizing the bulk email data program in 2004, the bulk phone call data program in 2006, and the wiretapping program in 2007.