Finding it hard to keep up the passion in a long-distance relationship? Help might be on the way.

A robotics professor in Singapore has invented a gadget equipped with motion-sensitive electronic "lips" that allow amorous but absent couples to exchange long-distance smooches via the Internet.

Shaped like a small head with oversize silicone lips, the "Kissenger" -- short for Kiss Messenger -- was unveiled in June at a scientific conference in Britain and is still being refined for commercial launch.

"It can be used between humans to improve their communication," its creator Hooman Samani told AFP.

Couples just have to connect the devices to computers via USB cables, link up online and start kissing the silicone material to trigger sensors that move the gadget on the other side.

They can stare at each other on screen while exchanging kisses.

"The main issue is to transmit the force and pressure, and also the shape of the lip," Samani said.

The "special silicone material" chosen for the lips offers "the best sensation and feeling", said the scientist, who has personally tested the device.

But the Kissenger is not yet ready for the market despite "a lot of offers" from interested parties because there are "ethical issues" that need to be resolved on top of the technical aspects, he said.

"Kissing is very intimate so in order to have a product in market which is going to deal with this sensitive issue we have to do proper studies and investigation on the social point of view, cultural point of view," he said.

The device is still being refined at a laboratory jointly set up by the National University of Singapore (NUS) and Keio University of Japan.

Samani calls his field of study "lovotics" -- research into the relationship between robots and humans -- and the Kissenger is just one of several devices being developed by his team.