Why the sleep data is not accurate?

The way our algorithm is designed is to track movement during sleep under typical sleep hours (6:00 p.m. - 6:00 a.m). If you are sleeping outside of a typical sleep hour range, the tracker will not record or display your sleep.
Sleep detection is mainly based on "body movement" + "heart rate". Body movement refers to physical activity, more specifically, the wrist activity of wearing band/watch (so there may be differences in the results of wearing sleep). When the body movement is small and the heart rate is low during sleep, it is considered as deep sleep. Conversely, when the body movement is vigorous and the heart rate is high, it is considered as light sleep.