Combining all that you need to run, the run pack features the Wahoo Key and the Wahoo Fitness soft heart rate belt in a convenient bundle. Wahoo Fitness wirelessly connects your iPhone 3G, iPhone 3GS or iPhone 4 to your favorite fitness measuring devices, including your heart rate sensor. With the Wahoo Key, your iPhone, your favorite playlists, the best fitness apps (321Run) and real-time activity information are all in the palm of your hand... or strapped to your arm.