Forget about using a pen to sign a credit card slip, or even tapping in a secret number. In the future, you could authorise payments by simply moving your finger over your flexible friend.
By Alfred Hermida
BBC News Online technology editor
A leading professor at the Massachusetts Institute of Technology has suggested using radio tags in credit cards as a kind of virtual signature.
A coil inside the card would act as the radio transmitter
Professor Ted Selker said the way someone moved their finger over the card would alter the radio transmission, producing a signal unique to that person.
"I could have some gesture and that would be my signature," he said, "it would be like a personal handshake."
The idea of putting radio tags in credit cards is not as far-fetched as it sounds. Mastercard has been experimenting with the technology, known as Radio Frequency Identification (RFID).
RFID tags are tiny transponders that send out radio signals and some experts predict they will become commonplace over the next decade or so.
The use of the technology in credit cards has been tested by Mastercard. Last year it ran a nine-month pilot in the US, involving some 15,000 consumers.
People could pay for goods by waving their cards near special tills, which would receive the information transmitted by the cards.
Prof Selker has suggested taking the technology a step further and using the properties of radio waves as a security check.
"By watching a finger moving around an antenna, we can literally see that the finger changes the antenna's behaviour," he told BBC News Online.
"I could draw letters and it would tell just by where my finger is how that is affecting the radio signal, whether or not it was me."
He suggested this could be used to make a RFID system that could complement or replace other ways of authorising a credit card.
"Wouldn't it be great if we could get the protection of having a personal identification number, without having to have a pad to type it into?" asked Prof Selker, who heads the Context Aware Computing group at the MIT's Media Labs.
"Wouldn't it be nice if something better than my signature would be transmitted without me having to use an external device?"
Civil rights groups have expressed concerns about RFID technology for some time. They worry it means people could, in theory, be tracked by the tags.
"You don't necessarily want a credit card that can be detected when you are not using it," said technology expert Bill Thompson. "You want a button that can turn it off or on."
"Otherwise imagine if you are a thief, you just wander around with a RFID detector looking for people with these credit cards."