I totally get with the prepaid oyster that when it’s topped up I’m physically touching it to the contact so the data is transferred, but with a debit card (especially if I’ve say paid for something online) how does it know what’s on the card ?)
In: Technology
It asks the bank. It has internet, it has your card details, it can just ask for X amount to be temporarily locked and see if the result is success.
The same way card machines in shops know, they talk to the bank. It’s really the same stuff, just with ‘working out the price’ coming after tapping instead of before.
From the little experience I have with it it _doesn’t_ know. It will try to block 1 pound once a day and after that it will not try to do any more transactions, only adjusting that one pound to the actual amount next day. If at that point you don’t have enough money you might go into negative on your bank account. Same if you tip in an American restaurant I guess.
It doesn’t. But there are servers that do. And you talk to them and get “yes, Mr Smith can afford two pounds” back.
You can also do this slightly delayed to speed people up through the queue, as losing two pounds isn’t a very big problem, so you just verify that the card is an actual card and let people through, then debit the account a couple of seconds later.
It’s the same as the oyster card, you just talk to the credit card company instead of the oyster server.
Basically, only familiar with this from the week I spent in London for my birthday. When I tapped in every morning, it would “reserve” some money in my account and then let me through. Much like a deposit. At the end of the day, sometime past midnight, the price would get adjusted and the payment executed. At least that’s what my banks reported on all three of my cards
It does not. The way it works is that it will always allow you to tap in if your card is not blocked by the TfL systems.
After a few seconds it will charge you £0.10 to make sure that your card is active. On the next day it charges you the relevant amount for the travel you have done.
If at any point they try to charge you and you have insufficient funds the card details go into their block list and is not allowed to be used again unless your debit is paid.
By doing it this way they ensure very fast processing and the only risk for them is someone using a card that does not have enough funds for a day’s journeys and never use that card again. So in the bigger scheme of things, minimal risk.
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