A German company plans to broadcast adverts via train windows so the sound appears to come from inside a person’s head when they lean against them.

The technology uses bone conduction, which transmits sound to the inner ear by passing vibrations through the skull.

The concept has been designed on behalf of Sky Deutschland by ad agency BBDO.

Chief executive officer of BBDO Sebastian Hardieck explained how it works: “Normally, the sound waves come through the air and through the ear to the inner ear where the waves are interpreted as sound. With bone conduction this works in a totally different way, a bone in the body is made to vibrate, it can be any bone, and the ear then interprets this high frequency vibration as sounds. “

Bone conduction has previously been used in hearing aids and headphones for swimmers and runners.

But it’s proposed use on the train is proving controversial.

One passenger said: “I think it is horrible. Really bad. We are already flooded with advertising. And I think when you look at this than you realize how far we have fallen in to a consumer society.”

Another added: “I can imagine when everyone is going to work in the morning, everyone wants to sleep then. And then just when you fall asleep you get even more advertising. I think there would probably be a lot of opposition to that.”

Google also plans to use the technology in its glass headset – another device which is proving divisive.