[Mike] sent in a different sort of hack – as part of the switched on London festival, these guys added bluetooth sensors to London Bridge. When a bluetooth enabled device is detected on the bridge, a blue ‘pixel’ will show up on the upper tower bridge. Once the device is detected at the other side of the bridge, the ‘pixel’ will move across the bridge at the same speed as the device did. You’ve got a few more days to check it out if you’re in the area.

Update: Just to be clear – the sensors are on the new London bridge, and the pixel/light appears along the top of Tower bridge. Sorry for the confustion, I haven’t been in London since 1995 or so. I mistakenly assumed that the lights were on the upper tower of the bridge.