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. What is Wahoo Fitness? Wahoo Fitness products wirelessly connects your smartphone to fitness sensors. With Wahoo Fitness, your phone, the best fitness Apps and real-time activity stats are all in the palm of your hand - or on your arm, or mounted on your bike. smart phone. smarter athlete. Wahoo Blue HR Heart Rate Strap for iPhone 4S Wahoo Fitness Blue HR heart rate strap is the world's first Bluetooth Smart heart rate strap made for the iPhone 4S. This heart rate strap and App combination transforms your iPhone into an all-in-one training device, great for runners, cyclists, and other fitness enthusiasts. The Wahoo Fitness Blue HR heart rate strap connects wirelessly to the iPhone 4S without the need for any adapters and delivers accurate real-time heart rate data through the free Wahoo Fitness App. Additionally, our open API allows other popular Apps, such as Strava, RunKeeper, MapMyRide, Cyclemeter, MotionX-GPS, and 321Run to work with the Blue HR. With the Wahoo Blue HR and your favorite fitness App, you now have your heart rate data, your playlists, your phone, GPS maps and more-- all in one device! This device will not work with the iPhone 3G, 3GS or 4. Features comfortable, elastic fabric strap to minimize chance of chaffing strap can be hand washed accurate and reliable records data even when receiver communication is interrupted two-snap connection is easy and fast and includes adjustable length strap sends and receives signals up to 10 feet unobstructed compatible with the iPhone 4S and iPad 3 waterproof up to 5 feet replaceable 3 volt CR2032 coin cell battery Wireless Bluetooth Smart Weight Sensor Pod: 17 grams {0.6 ounces} Strap: 28 grams {1.0 ounces} Total: 45 grams {1.6 ounces}