Tim Woodall wrote:
What screen? All I've ever seen is a green and red light.

p.s. Does anyone know what happens if you try to badge two oyster cards
at once? I've thought about getting a second card so when one runs out
of cash I can then use the other one to get me to somewhere where I can
top up. What about if I wrap the "backup" card in aluminium foil?

As far as I am aware, some form of screen exists on all gates and
validators, whatever their design. Certainly on the old pneumatic
gates the information pops up on the glass panel toward the top of the
gate, where the green entry arrow is illuminated, and tells you either
your current balance or "ticket 1 near expiry" if you have a season
ticket. This is the same place where it tells you "seek assistance" if
its giving you grief. Other designs have this in a different place -
If I remember right, I believe the newer gates like those in Kings
Cross (coming off the Picc) have it on a small LCD display by the
Oyster reader.

In answer to your second question, two Oysters together will be
rejected by the gates. The same applies with some smart passes people
carry for work, or even some credit or other personal cards can
interfere with the Oyster, which essentially contains a small chip and
a thin wire wrapped round its inside as an aerial. As for foil... I
can't see it making a difference. Do what some people I know do - have
two wallets, clearly marked as "work" and "personal" or something like
that.