It is a transmitter+ a receiver swim training gadget 

with bone conduction headphone, solves the communication problem 

between swimmer and coach during training. The Bone Conduction

headphone provides the best quality sound, a stylish design, and

is our most popular product. It carries an IPx10 waterproof rating

and is available in several stunning colors.

It is astounded for deaf at the difference in sound from using these headphones.

http://www.szrisest.com