Meet the Kuai: waterproof sport headphones with a heart rate sensor, accelerometer, 8 GB of memory, and smart coaching. It measures your speed, cadence, strokes, calories, and VO2max. You get training plans for running, swimming, and cycling.
The device has up to 7 hours of battery life. It works autonomously or with your ANT+ / Bluetooth devices. Costs under $200 at this time.