GPS model lets you take calls and reply to texts from your wrist Measure your blood oxygen with an all-new sensor and app Check your heart rhythm with the ECG app The Always-On Retina display is 2.5x brighter outdoors when your wrist is down S6 SiP is up to 20% faster than Series 5 5GHz Wi-Fi and U1 Ultra Wideband chip Track your daily activity on Apple Watch and see your trends in the Fitness app on iPhone Measure workouts like running, walking, cycling, yoga, swimming, and dance Swimproof design Sync your favorite music, podcasts, and audiobooks.