FINIS Swim Coach Communicator,

Patented bone conduction speakers deliver crystal clear audio through the cheekbones to the inner ear, without the Use of earbuds. Place on your Temple bones (not over your ears)
Allows coaches to provide swimmers with real-time stroke corrections, pace, splits and more.
Uses Bluetooth transmission from your Smartphone to the device's receiver – keep the receiver above the water for a successful signal.
All you need is a smartphone – simply download the FINIS live mobile application, and use The microphone to communicate with your swimmers.
Waterproof IPX8 (up to 3 meters) and rechargeable lithium-ion Battery.