the Secret Service, and the tapes were stored in a room in the White House basement. Significant phone lines were tapped as well, including those in the Oval Office, Old Executive Office Building and the Lincoln Sitting Room, which was Nixon's favorite room in the White House. Telephone conversations were recorded by tapping the telephone lines from the White House switchboard and relaying the conversations to recorders in a closet in the basement of the residence. All audio equipment was sound-activated, except in the Cabinet Room. All locations in the White House were activated by the Executive Protective Service's "First Family Locator" system: when an officer notified the system that the president was in the Oval Office, the taping machinery switched on, ready to record when triggered by sound. By design, only very few individuals (apart from Nixon and Haldeman) knew of the existence of the taping system: Butterfield, Haldeman's assistant Lawrence Higby, and the Secret Service technicians who had installed it. The recordings were produced on as many as nine Sony TC-800B machines using very thin 0.5 mil (12.7 µm) tape at the slow speed of 15/16 inches (23 mm) per second. The tapes contain more than 3,000 hours of conversation. Hundreds of hours are of discussions on foreign policy, including planning for the 1972 Nixon visit to China and subsequent visit to the Soviet Union. Only 200 of the 3,500 hours contain references to Watergate and less than 5% of the recorded material has been transcribed or published. Revelation of the taping system The existence of the White House taping system was first confirmed by Senate Committee staff member Donald Sanders, on July 13, 1973, in an interview with White House aide Alexander Butterfield. Three days later, it was made public during the televised testimony of Butterfield, when he was asked about the possibility of a White House taping system by Senate Counsel Fred Thompson. On July 16, 1973, Butterfield told the committee in a televised hearing that Nixon had ordered a taping system installed in the White House to automatically record all conversations. Special Counsel Archibald Cox, a former United States Solicitor General under President John F. Kennedy, asked District Court Judge John Sirica to subpoena nine relevant tapes to confirm the testimony of White House Counsel John Dean. Saturday Night Massacre President Nixon initially refused to release the tapes, putting two reasons forward: first, that the