Fitbit Charge Hr. New. Replacement sent out by fitbit. Size small. Black. Charge HR is sweat, rain and splash proof. However, the device is not swim proof or showerproof. With any wearable device, it’s best for your skin if the band stays dry and clean. Charge HR tracks your heart rate all day and during exercise. Charge HR can receive notifications for phone calls. Charge HR will vibrate and show the name or number of the caller.