I recently bought the Mi Band from Ali Express and the Heart rate monitor was not working out of the box for some odd reason but I found a fix for that in this article-
I DO NOT GUARANTEE THAT IT WILL WORK FOR EVERYONE BUT IT DID WORK FOR MANY!
- Uninstall the latest Mi Fit which you installed from Play Store.
- Reboot the phone
- Install Mi Fit 2.2.9 ver 3113 from HERE!
- Log in to the app
- Wait for the Mi Band 2 to synchronize
- Go to find update in Profile – Settings- Check for updates
- Install the updateLaunch the newly installed app & Hurray! Heart Rate monitor should start working on your MiBand 2 again!
Few extra tips
Hold the Miband tight to your hand in order for it to work most of the times.
It may not work always so beware of that and only Xiaomi can fix that.