The HRM 200 heart rate monitor transmits accurate real-time heart rate and heart rate variability data to compatible Garmin smartwatches and cycling computers, fitness equipment, and apps Comfortable strap is available in two sizes (XS–S and M–XL) for the most ideal fit for your body type Up to 1 year of battery life with a user-replaceable battery Durable and built to last with a 3 ATM water rating Machine washable for easy cleaning XS-S: Fits chest circumferences 60-85cm (23.5" - 33.5") M-XL: Fits chest circumferences 80-119cm (31.5" - 47")