In message , at 12:59:12 on Sat, 26 Feb
2011, tim.... remarked:
I must admit I wasn't aware of the autocomplete feature of Oyster.

I've never heard of it before.

When there is a football match for example they open the
barriers and implement something called "autocomplete".

That means the system in effect touches you out of the system
automatically without you having to do it. Sensors pick up cards
going through the barriers.

The problem is that to make sure your journey is completed by
the system you have to touch in at the same station within three
days. Or you get a maximum fare.

Speculating, they seem to be able to *read* the cards as you walk past
the barriers (feet away from the sensors perhaps) but can't *write* the
appropriate "touch-out refund" to the card. So save it up on that
specific gateline only, for three days, in case you happen to be able to
pick it up.

Of course, they could instead put this into their "you have a refund to
pick up" system. Or is this snake oil? (especially the 'reading at a
distance' part?)

They can't be "read" at a distance as they need the local RF loop to power
them.

They can be "overheard" at a distance if another device is already reading
them, but this isn't the case here.

(we need some real technical words for those two things. I have no idea if
there are some already in common usage!)

So what *is* the action they refer to as "picking up cards going through
the barrier"?
--
Roland Perry