With the Garmin HRM 200 Heart Rate Monitor Chest Strap Black M-XL, you can accurately measure your heart rate when you work out. you can read your heart rate right away on your smartphone, sports watch, bike navigation, or fitness machine. You can connect these devices to your HRM 200 via ANT+. This information is locked, so your information stays safe. The chest strap is adjustable from 80 to 119cm chest circumference. With a smaller chest circumference, go for the XS-S model. The heart rate sensor can withstand rain and sweat, so you can work out when it rains without problems. The sensor isn't waterproof, so you can't swim with it.