"David Boothroyd" wrote in message
...

What I wonder is whether it's possible to search for a specified Oyster
card chip in the neighbourhood by stepping up the power of a detector.
It's
done on RF so it's not totally impossible that all you would need to do to
find one is have a suitably sensitive detector and then it wouldn't matter
whether someone used the card.


but then how would it get feedback from the card?