The Mi Band 2 is not embedded smart alarm clock, so use XSmart mode:
It works on the side of the phone, so it requires on bluetooth connection to the phone. Phone for 30 minutes (the time can be adjusted) to set the alarm starts to synchronize with the bracelet every minute, and then determines the phase and wakes up when a phase of light sleep. Awakening vibration and the sensitivity of the detection light sleep can be adjusted. The program and bluetooth does not need to keep running.
Please help me translate that program into your language on https://www.localize.im/projects/vl