[ultrafez]

I believe it's down to how your bank sets up your card, and how the retailer's set up. In the UK, when I pay with my debit card at Tesco, after entering my PIN it instantly says I can remove my card. Apparently it's because the card reader skips communicating with my bank until they cash up at the end of the day (the "available balance" of my card doesn't reduce after shopping there until the next day). Tesco is the only retailer where I've seen the card work almost instantaneously, but I expect that NFC payments work that way every time.

[brianwawok]

How do they detect invalid or cards with no balance? Seems you have to round trip to the bank at least once or you would be no better off than checks.