64-bit dual core S5 processor 957 sq mm display area Second-generation optical heart sensor Digital Crown with haptic feedback, GPS model lets you take calls and reply to texts from your wrist Large Retina OLED display Up to 2x faster processor than Series 3 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 High and low heart rate notifications and irregular heart rhythm notification Sync your favorite music, podcasts, and audiobooks Built-in compass and real-time elevation readings Can detect if you’ve taken a hard fall, then automatically call emergency services for you