I'm not sure I'd describe it as a *technology* failure. The passenger
has presented a set of cards to the reader, two of which have validity
for the journey. What do you expect to happen in those circumstances?

A properly designed system would instruct the cards to back-off for a
pseudo random period, then interrogate again.

I still don't understand how that tells it which of the two valid
cards to use.

On the theory that the fairly bad always triumphs over the good, I
expect the solution will be tin foil hat wallete with an external
pocket. My wallet has internal shielding on each card pocket so that
none of the cards in it are visible to external readers. It would not
be hard to make a modified version of such a wallet with one pocket
deliberately left unshielded, so you can use it to touch in without
removing the card from the wallet.

I understand all the reasons such an approach stinks, e.g., for people
who use the Oyster to get to work and a company ID to unlock the
office door, but you heard it here first.

--
Regards,
John Levine, , Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. http://jl.ly