Room 641A, Surveillance facility in San Francisco, United States
Room 641A is a monitoring facility inside a telecommunications building in San Francisco, California, United States. The space measures roughly 24 by 48 feet (7.3 by 14.6 meters) and contains multiple equipment racks housing Narus STA 6400 network analysis systems that process internet data streams in real time.
The facility was built in 2003 as part of expanded monitoring programs following the September 11 attacks in 2001. AT&T installed the equipment and connected it directly to major internet backbone routes passing through San Francisco.
The designation comes from the original room numbering system at the 611 Folsom Street building, where technician Mark Klein brought the monitoring station to public attention in 2006. His disclosure sparked nationwide debates about government access to digital communications and shaped public awareness of privacy concerns for years to come.
The facility sits inside an active communications building with no public access. Visitors can view the exterior of the building on Folsom Street in the South of Market neighborhood, where several telecommunications hubs are located.
Fiber optic splitters divert data packets from international and domestic connections without interrupting the flow. This passive technique allows all passing information to be captured and analyzed in parallel with normal transmission.
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