Wahoo Fitness Stride Sensor for iPhone
Capture accurate speed, distance and stride rate data while you run, walk or hike.  The Wahoo Stride Sensor transmits this data to your iPhone when paired with the Wahoo Key or any other ANT+ adapter. The Stride Sensor is a great companion for your indoor treadmill runs – you can finally send speed, distance and stride data directly to your iPhone while on a stationary treadmill.