Bone Conducting Spatial Audio Sound Tracks Via Vibrating Windows

Bone conduction occurs when sound is channelled to the inner ear through the bones of the skull. World famous Classical music composer Beethoven went completely deaf in his later life and relied on creating his compositions, by dismantling his piano, laying out on the floor then leaning the side of his face on the floor. This was possibly the first documentary evidence of someone listening to sound by bone conduction.
These days bone conduction techniques are becoming more commonplace with advances in signalling technology giving rise to  headphones, and hearing aids, among which there are specialized communication products such as a bone conduction speaker that is used by scuba divers. More recently is the Google Glass device for the relay of information to the user through a microphone that sits beside the user's ear.
But BBDO Germany is taking this technology a step further with highly specialized device attached to the windows of public transport that silently transmits high-frequency oscillations that your brain converts into sound.
Demonstrated in the following video we see travellers on a train leaning their heads on the train's windows possibly through boredom and or catching up some dozzie sleep but become quietly alarmed by a sound track perceiving to be working like voices from within their heads.

The sole purpose of this technology was to discover ways to perpetuate a new form of advertising, but in sum, although one's boredom may in some small way be alleviated it also  suggests a new form of invading or challenging one's privacy ?