The Apple watch Series 8 is a minor upgrade from the Series 7, with a new temperature sensor and improved motion detection. The Series 8 has the same design, display, battery life, and performance as the Series 7, and supports the same apps and features. The temperature sensor can measure your skin temperature and alert you of any changes, but it requires a separate app and subscription. The improved motion detection can track your fall risk and detect car crashes, which can be useful for safety and emergency situations.