Someday consumers may find themselves listening to paper to learn more about products, receive instructions or heed warnings. That's the hope of Swedish researchers studying ways to print loudspeakers and keyboards on paper.

But the researchers, who have shown how to use printable ink instead of wires or other embedded devices like chips in greeting cards to communicate signals on paper, concede that without a way to print the interactive paper cheaply, their invention may never leave the lab.

"Our prototype is handmade, which makes it expensive" but the idea is to be able to print on a large scale, Brink said. "That would make it cheap."

A new research phase starting later this year will focus on using interactive paper in packaging, said Brink. This phase follows the construction and successful testing last month of a prototype display that provides information about tourist attractions and examples of CD recordings.

Finding ways to prevent messages from being unintentionally activated is a challenge researchers face as they tinker with interactive packaging. Store clerks and shoppers, for instance, could become annoyed by products they handle constantly speaking to them. "This is something that will have to be looked at," Brink said.

The current prototype uses an electronically conductive ink that responds to pressure, by a finger or hand, for instance. It also uses printed speakers created with the conductive ink spread over a material-- in this case aluminium foil-- which covers an empty cavity to form a diaphragm. The areas covered by the conductive ink are linked at the edge of the paper to wires, which relay the signals to a chip embedded with audio files.

The prototype display consists of three different layers of paper. The back of the display is made of cardboard. The middle layer is printed with the conductive ink on regular paper. And the top layer, the "skin," which uses paper designed for glossy pictures, contains the graphic elements, such as pictures of cities and CDs. The skin layer is also used to cover the conductive ink.

The system works like this: When you touch, say, a picture of a new CD recording, the pressure of your hand or finger sends a signal, which is captured by the wire at the end of the paper and forwarded to the chip. The chip, in turn, activates an audio file, which is streamed through the printed speaker also connected to the wire and conductive ink system.

The paper printed with the conductive ink can be recycled or thrown away.