Getting detailed data about your workouts is great and all, except there's so much cumbersome gear involved. A chest strap for your heart rate, your phone to track distance and play music, some headphones so you can listen to music in the first place and hear your training app's voice prompts.
Chest strap heart rate monitors are uncomfortable and annoying. HRM watches, like the MIO Alpha, have a lot of potential, but they still lose contact frequently. Valencell is going in a different direction, building a heart rate sensor into something most of us are already wearing: our headphones.