Scales

There are many scales that can store you weight readings "in the cloud".

Many of these scales work using Bluetooth low energy (BLE), so it be possible to reverse engineer their protocol and use this data outside of the apps they provide.

A third party open source program was been written for extracting data from the Medisana BS 440 and is available here https://github.com/keptenkurk/BS440. The author says that these approaches may well work for other medisana scales. This approach way well generalise to other scales, but will likely require some tweaking.