On 22 Jul, 13:39, " wrote:
It depends on whether all the card transmits to the gate is the serial
number or whether it includes some extra information - e.g. last gate
to have gone through and whether that can be checked by the central
system. I've not looked into how oyster works at all - I don't know
whether the gates rely on a real time connection to the central system
or not.

The card has its own memory and enough information onboard that it can
be authorised/charged/whatever without checking any central databases.
Ticket barriers are online (i.e. have a live network connection) but
it would be impractical for them to check a central database during
every touch. Bus ticket machines are offline and rely on nightly
downloads at the depot. Not sure about standalone validators and other
edge cases.

I wasn't considering reading it from more than an inch away. That's
why I said a crowded station. If you need to read a card then you just
stand near to the exit gates and watch until you see someone pass
though and then stick the card in an easily accessible point. You then
"accidentally" bump them. Now you've got whatever information the gate
was expecting to see on the next trip.

I think it's been demonstrated that passive cards (like Oyster) can be
read from at least a few feet away with the right equipment.

U

--
http://londonconnections.blogspot.com/
A blog about transport projects in London