The US Department of Homeland Security, along with Boeing Intelligence and Security Systems, is fielding sensors on the border with Mexico, in an $8 billion project called the Secure Border Initiative network, or SBInet.
SBInet will eventually comprise some 400 25-metre-high towers similar to cellphone masts and containing an array of remote-controlled optical and infrared cameras. The towers will also carry a primary sensor designed to detect humans. This will all supplement ground surveillance radar and vibration sensors.
Around the world, other countries are also deploying technology to monitor their borders.
Full story from New Scientist