Google's new augmented reality glasses will use the human skull rather than speakers to reproduce sound, according to documents filed with US regulators.
The wraparound glasses, which are due for release in 2014, will allow users to bring up information on the screen by voice command, using the Android operating system run by a tiny computer in the glasses.
The glasses transmit audio waves down the ear channel and through bone tissue in the skull to generate sound.
Bone conduction sound technology is not new but has not been widely used for everyday products. Last year Aftershokz unveiled new headphones that employ it.
The technology is widely used by special forces and police during covert operations to prevent sound 'leaking' from headphones. It can also be used underwater using a device clipped on to goggles or incorporated into hearing aids.
Last month, Google filed a patent for spectacles that integrate bone conduction sound technology, and the Federal Communication Commission this week approved Google Glass, featuring an "integral vibrating element that provides audio to the user via contact with the user's head".
One advantage of the technology is that it allows wearers to hear sounds in their immediate environment, which could be a lifesaver for users crossing the road in a busy city.
The glasses feature WiFi and Bluetooth connectivity and will allow the wearer to see useful information without having to consult a smartphone or similar handheld device.
Google co-founder Sergei Brin has been snapped by a fellow passenger testing the new glasses on a New York subway.
Developers will receive the first finished models, and have been paid $1,500 to help refine the product before it is launched.