Compatible with: iPhone 4S and other Bluetooth Smart Ready devicesPart#: WFBTHR01Wahoo Fitness Blue HR heart rate strap is the world's first Bluetooth Smart heart rate strap made for the iPhone 4S (and other Bluetooth Smart Ready devices). 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 RunKeeper, MapMyRide, 321Run, Cyclemeter and endomondo 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: Wireless Bluetooth Smart Records Data even when receiver communication is interrupted Adjustable strap length Two snap connection on strap for easy use Water resistant up to 5 feet Sends/Receives signals up to 10 feet unobstructed Replaceable 3 volt coin cell battery (CR2032) Weight 45 g (1.6 oz.) Materials/Contents Strap : Comfortable elastic reduces chaffing. Hand wash.