The innovation is beginning to seep into consumer electronics. In the early 2000s, headphone sets appeared that played music via the user’s bones, but the systems were hamstrung by high cost and low quality, with common complaints about muffled and distorted sound. The makers of Aftershokz believe they have solved those problems with a unit that retails for $79.

“The difficulty has been in transmitting vibrations through bone with enough power to be musical”, says CEO Bruce Borenstein. “You need around 20,000 Hz to power the dual transducers, which has been our big breakthrough”.

The bone conduction system offers key safety advantages over traditional earphones, by leaving the user’s ears free so that they are not distracted from their environment. It is even possible to drive wearing them, as they comply with the legal requirement to be able to hear on the road.