The credit card companies are promoting cards that have instant pay systems. You’ve probably seen the ads, where the user just swipes the card over the instant pay terminal, and the transaction is done. No signing. No ID check. The sales person doesn’t even necessarily see the card.
Sounds great, but what happens if you lose the card? Won’t it be easy for someone who finds it to use it, at least until you report it lost? Sure, you are probably limited in what you will be liable for, if you report it promptly, but it will still likely be an annoyance to get the items off your bill. It would be much better if the card would stop working by itself after you lose it, automatically.
Idea: build Bluetooth into the cards, and let the user pair them with their cellphone. When the card is about to do a transaction, it can check for the cellphone. If it does not find it, it should not allow the transaction. That way, you’d need to lose both the card and your cellphone to allow the bad guy to use your card.