"The technology 'sees' the shapes made when radio waves emitted by mobile phone masts meet an obstruction. Signals bounced back by immobile objects, such as walls or trees, are filtered out by the receiver. This allows anything moving, such as cars or people, to be tracked. Previously, radar needed massive fixed equipment to work and transmissions from mobile phone masts were thought too weak to be useful."
Not enough detail in there to answer many questions - anyone have any more info on this? <http://www.observer.co.uk/uk_news/story/0,6903,811027,00.html>
