Here you will find all the files you need to build ESP-01 microcontroller and a reed switch to read your Krom-Schröder gas meter electronically.
Have a look at my video on Youtube:
https://youtu.be/i9hPf0uNzFE
Thingiverse - 3D-Model of the case:
https://www.thingiverse.com/thing:5152526