So you are a member of ZZ Top?

Check this: https://github.com/Stirling-Tools/Stirling-PDF

Since you are on Linux just Start it in a Docker container locally and you are golden :)

I have Nous A1T with Tasmota firmware (they are available pre-flashed) for the normal power sockets and Shelly 1PM for in-wall Installation. Both work with home assistant flawlessly.

Edit: Shelly tries to communicate with outside servers (cant remember exactly which one, might only be time server and update server, but unsure) so they are in a VLAN without Internet connection)

This is what I do. Monitor power consumption with home assistant and a 15 buck wifi plug. If the value falls below a certain threshhold for a few minutes, homeassistantt sends a notification to my app.

All local, no cloud, easy, cheap.