tracking systems that access carrier location databases are unusual in their ability to allow virtually any government to track people across borders, with any type of cellular phone, across a wide range of carriers — without the carriers even knowing. These systems also can be used in tandem with other technologies that, when the general location of a person is already known, can intercept calls and Internet traffic, activate microphones, and access contact lists, photos and other documents. Companies that make and sell surveillance technology seek to limit public information about their systems’ capabilities and client lists, typically marketing their technology directly to law enforcement and intelligence services through international conferences that are closed to journalists and other members of the public.