Hacking the Mi Band 3 - Part 1 : Reverse Engineering

The Mi Band 3 is one of the most popular, and arguably the best budget fitness tracker in the market right now. Released by Xiaomi in 2018 as a successor to the Mi Band 2 and Mi Band HRX Edition, it comes with a larger screen and a variety of new features.

This 3 part guide is going to be about hacking into and modifying the firmware of the band, which lets us customize the Watchfaces, font, logos, and animations to our liking.

Part 1 of this series deals with the reverse engineering of the band, that is finding a way to access the firmware and resource files.

Warning: Although there's an extremely low chance, we are not responsible for your band getting bricked, loss of data, void warranties, blown up batteries or World War III. You are choosing to do these modifications yourself and if you point a finger at me if something goes wrong, I will just laugh at you. (And maybe help you find a solution if you're a nice person).

Prerequisites

• Mi Band 3
• Latest APK of Mi Fit
• AmazefitBipTools
• 7-Zip

Step 1 - Unpack the Mi Fit APK

Right-click the APK file you downloaded, and extract it to a folder using 7-Zip as shown in the screenshot.

Step 2 - Copy the firmware files to another location

Navigate to  \com.xiaomi.hm.health_2018-11-05\assets 

Now copy the files

• Mili_wuhan.fw
• Mili_wuhan.ft
• Mili_wuhan.res

to another folder.

Step 3 - Decompile the resources file

Extract the AmazefitBipTools archive. Now, copy the Mili_wuhan.res file into it.

Drag and drop Mili_wuhan.res onto WatchFace.exe. This will decompile the resources into a folder.

Conclusion

We have now successfully decompiled the resource files from the Mi Fit app and can now access the icons inside in a .png format. 

We will deal with editing these resources in the next part of the series.