With the Garmin HRM-Fit Heart Rate Monitor Chest Strap Black, you get a lot of data about your heart rate during workouts. You attach this sensor to a sports bra. So you do need to wear a sports bra, or it won't measure your data. The heart rate chest strap measures your heart rate more accurately than a sports watch. You can read your heart rate right away on your smartphone, sports watch, bike navigation, or fitness machine. You can pair these devices with your HRM-Fit via ANT+. The heart rate sensor can handle rain and sweat, so you can use it without worry when it rains. It includes a replaceable battery that lasts about 3.5 years. After that, you can easily replace it yourself. Do you want a heart rate monitor with an adjustable chest strap? If so, choose the Garmin HRM 200 or 600.