Google's hotly anticipated new glasses- which will wearers to summon up maps and other useful data on a screen in the lens- will create sound by sending vibrations directly through the wearer's skull, it has been revealed.
The features are included in documents filed with American regulators, and show how the futuristic specs will use "bone conduction", which sends vibrations to the inner ear through the skull instead of speakers.
Though not a new kind of technology- Panasonic exhibited prototype bone conduction headphones at this year's Consumer Electronics Show- the process is yet to be widely adopted.
One of its advantage is that it allows listeners to hear the noise in the environment too.
The Federal Communication Commission this week approved the web giant's patent for Google Glass, including "integral vibrating element that provides audio to the user via contact with the user's head".
Google co-founder, Sergey Brin, is leading the development, and last month he was pictured testing Google Glass on the New York subway.
The glasses also boast Wifi and Bluetooth connectivity, and a small screen that appears in the wearer's normal field of vision. A tiny, voice-operated computer inside Google Glass runs the Android mobile operating system.
It is planned that wearers will be able to summon up maps and other useful data from the web straight on to their lenses.
The first complete Google Glass hardware will be sent to developers who have paid $1,500 to help refine the technology.
Google has said it hopes to introduce Google Glass commercially in 2014.