The Mi Band 5 or Band 4 has a software on board, which should enable you to record sleep phases. The sleep tracker should recognize when you are in a deep sleep or awake phase.
But if you have the problem that the fitness tracker does not record your sleep cycle correctly, it is time to check various settings and eliminate sources of error. The following workarounds should help you:
Mi Band 5 or Band 4 does not record sleep data - Solution
The following two settings should be checked in connection with a faulty sleep recording:
Disable battery optimization for the Mi-Fit app
In Android, in connection with the energy saving management, there is the possibility to restrict the background data for certain apps or to put apps into a sleep mode. It is possible that if the connected Mi Fit app is put into sleep mode the sleep detection does not work correctly.
To check this, please go to the energy management of your smartphone and set the appropriate settings for the Mi Fit app.
As a quick solution you can also try to switch off the energy saving mode.
Battery of Mi Band 5 or Band 4 should not fall below 25%.
Below 25% percent battery power the heart rate monitor is only used in a reduced way. This leads to the fact that the sleep detection no longer works so well. Therefore: The Mi volume 5 or volume 4 simply before sleeping go again charge.