The Suunto Smart Heart Rate Belt provides accurate heart rate data without compromising comfort. The belt provides superior performance in sports where hand movement disturbs wrist heart rate measurements and allows measuring heartrate wearing the watch on top of the sleeve or attached to the bike handlebar or even not carrying the watch at all during the exercise.? The Suunto Smart Heart Rate Belt has an R-R memory that is used when the watch is not within reach of the Bluetooth smart radio. This is great for example in team sports where it allows recording without wearing the watch. The memory function is supported with the Suunto 3, 5, 9, Spartan, Ambit3 and Traverse watches.? Biking, team sports, martial arts, climbing, swimming, water sports, triathlon, ski mountaineering, cross country skiing, skating and gym enthusiasts will see the greatest benefits from using the Suunto Smart Heart Rate Belt.? The Suunto Smart Heart Rate Belt is also a great companion for the free Sports Tracker app with Android, iOS and Watch OS devices.? ?The belt included in the package is black size M. You can purchase a spare Suunto Chest Strap separately available in sizes S, M and L.