Bone conduction headphones, unlike normal headphones, use the skull bones to propagate sound by emitting small vibrations on the bones between the jaw and the mandible, close to the ear, leaving it free at the same time to hear the sounds coming from the surrounding environment. These types of headphones can lead to a complete isolation from what is around you, which is why they are widely used by runners. The benefits are many:  they do not damage the eardrums and do not obstruct the ear canal, thus avoiding problems with the apparatus;  by transmitting the sound directly to the cochlea, they can be a good solution for people with hearing problems or with tinnitus, because they avoid creating a resonance chamber that could accentuate the problem.