what are the features of apple watch series 1?
['38mm or 42mm case.', 'Retina OLED display with Force Touch.', 'S1P with dual-core processor.', 'Digital Crown.', 'Optical heart sensor.', 'High and low heart rate notifications and irregular heart rhythm notification.', 'Splash-resistant 9', 'Wi-Fi and Bluetooth 4.0.']