The Wahoo Fitness Blue HR heart rate strap works with a number of i OS apps to convert your iPhone, iPad or iPod Touch into a an all-in-one training device, great for fitness enthusiasts. The strap utilises Bluetooth technology to wirelessly communicate with your i OS device & delivers accurate, real-time heart rate data through the free Wahoo Fitness App. The strap is comfortable to wear, with the use of elastic designed to prevent chafing. The two-snap connection is easy, adjustable & fast so you can ensure the strap is safe on your arm. It is also waterproof up to 5 feet, so theres no need to worry about sweat damaging the equipment. Signal can be sent up to 10 feet, so you can keep your device safely to one side when you train on a treadmill, cross-trainer or other exercise machine. Works with a number of apps, including Strava, Run Keeper, Endomondo, Map My Ride, Cyclemeter, Motion X-GPS & 321 Run as well as the Wahoo Fitness App. iPhone 4S, iPhone 5, iPad (3rd & 4th generations), iPod Touch (5th generation) Requires CR2032 battery