These headphones use the bone-conduction to transit sound. Normally, air vibrations are transferred to our eardrums, which convert the signal into sound to the brain. With traditional headphones/earplugs, the vibration can damage the ear.

The Outi uses bone conduction (cartilage is the actual medium here) to transmit sound. It clips to the ear lobe, which is unusual, but very unlikely to cause ear damage. It is said to have a very intense perceived bass, but we have not tested it, yet.

[Via]