RFID tags are already used in smart cards such as the Oyster ticket used to travel on public transport in London.

They have also been incorporated into the new biometric passports introduced recently by the UK government.

But these devices are based on silicon and are too expensive for use in everyday applications such as tagging items in a supermarket.

Now researchers at Rice University in the US have colloborated with colleagues at Sunchon National University in Korea to create RFID tags that can be printed onto a roll of plastic.

Printable RFID tags are practical because they're passive in nature -- they power up when hit by radio waves at the right frequency and return the information they contain.

"If there's no power source, there's no lifetime limit," said Professor James Tour of Rice University.

"When they receive the RF signal, they emit."

Before the tags are ready of use outside the lab, researchers must find a way to reduce the size of the tags by two-thirds to match existing bar codes.

There are also issues around the range of the tags.

"Right now, the emitter has to be pretty close to the tags, but it's getting farther all the time," Professor Tour said.

"The practical distance to have it ring up all the items in your shopping cart is a metre."

"But the ultimate would be to signal and get immediate response back from every item in your store -- what's on the shelves, their dates, everything."

"At 300 meters, you're set -- you have real-time information on every item in a warehouse."

"If something falls behind a shelf, you know about it."

"If a product is about to expire, you know to move it to the front -- or to the bargain bin."