London's Tower Bridge, as a Bluetooth device !

For a week, some company has transformed the famous Tower Bridge into the world's largest Bluetooth device. Using multi-colored lights strung across the length of the upper walkway, technicians have created a gigantic interactive exhibit wherein sensors located at either end detect travelers' Bluetooth-enabled gadgets (cellphones, laptops, PDA's, GPS, etc.) and then track their progress in pseudo-real-time as they move across the bridge. Visually, the movement is represented by a uniquely-colored pixel appearing at more-or-less the same spot on the walkway as the device; to a faraway observer, it would look like this single "pixel" was making the journey from one end to the other... see the full article at http://www.hackaday.com/2007/02/14/bluetooth-enabled-london-bridge/