I recently bought the ‘smart’ body fat scale Crénot Gofit S2. As many of those modern ‘smart’ devices it uses
Bluetooth Low Energy
(BLE
) and an App on the phone to connect to it. Due to privacy concerns I do not want to use this
cloud based App and share my fitness / health data.
Instead I found openScale. An open source App which would give me the same functionality while storing all data locally on my phone. Sadly it did not support my scale so I started investigating if I can add support for it.
Initially I read the How to reverse engineer a Bluetooth 4.x scale notes on the openScale Github page and also created a Bluetooth HCI snoop log as described there, but then ended up following a different approach and wrote a small client in Python by using Bleak.
BLE devices use the Generic Attribute Profile
(GATT
) and provide services with different characteristics.
The BLE scanner App mentioned in the notes
became handy to gather information about the scales provided services and characteristics.
With this information I quickly was able to reliably get the weight value from the scale but did not figure out yet how other values - like body fat percentage for example - are transferred.
My client can be found in my scale-communication repo on Github and with knowing the basic communication protocol it also will be possible to implement this in openScale. I also did not give up yet on getting the missing values from my scale - but that’s for another time.