Meet the Shapeheart Armband: a smartphone holder that also makes it easy to keep an eye on your heart rate as you exercise. Its magnetic phone case keeps your device secure as you run. You also get a removable optical sensor with 25 hours of battery life and Bluetooth.
You will be able to use this with your favorite running apps. The armband is adjustable and has a touchscreen window to let you interact with your smartphone easily. Devices from 4″ to 6.2″ are supported.[where to get it]