Apple Watch Series 4 40mm Silver Stay connected, stay informed, and remain healthy with the Apple Watch Series 4. This Apple Watch features a 40mm curved watch face with an LTPO OLED Retina display and digital crown. The crown is how you navigate through watchOS 5 to view your apps and content. The crown has haptic feedback, giving each turn a mechanical click-like feel, and an integrated titanium electrode lets you use the ECG app. On the back, the Apple Watch features an optical heart sensor to quickly check your heart rate, and an electric heart sensor that works with the crown to generate an ECG (electrocardiogram). Improved Sensors Generating your own ECG to save and share with your doctor is just one example of how the Apple Watch is designed to help you monitor your health. It can also detect and monitor your workouts, giving you essential metrics to help you reach your goals. It's water-resistant up to 164', so you can record laps on a track or in the pool. Even when not working out, the Apple Watch utilizes three activity rings to motivate you to keep moving throughout your day. You can help stay motivated during workouts by streaming your favorite music, podcasts, or invite a friend to a seven-day challenge. In a competition, you'll share your activity and compete for bragging rights and digital medals. Notifications of your friend's progress act like a personal trainer to keep you going. The Apple Watch Series 4 stays connected to the outside world via Wi-Fi or a wireless Bluetooth connection to your iPhone. When connected, you can use the watch as an extension of your phone to view text messages, interact with Siri, navigate via built-in GPS, or make hands-free calls with the integrated speaker and microphone.