Apple Watch Series 5

The always-on display is the change that made the Apple Watch a watch. Every model before it went dark when your wrist dropped, so checking the time meant a deliberate gesture, which is a strange thing to ask of a watch. Apple used an LTPO panel that drops to 1Hz when idle, refreshing once a second instead of sixty times, and held the same 18-hour battery life. A compass arrived. So did international emergency calling, working in over 150 countries whether or not you have a cellular plan there. Everything else came from the Series 4. It is the smallest change in the line that made the largest difference to how people use it.