Check your heart rate

For best results, the back of Apple Watch needs skin contact for features like wrist detection, haptic notifications, and the heart rate sensor. Wearing Apple Watch with the right fit—not too tight, not too loose, and with room for your skin to breathe—will keep you comfortable and let the sensors do their job. You may want to tighten Apple Watch for workouts, then loosen the band when you’re done. In addition, the sensors will work only when you wear Apple Watch on the top of your wrist.