Modem state and signal monitoring

[black-roland]

Feature request from comments:

Is it possible to add a binary sensor to your integration that reflects the “liveness” of the modem? I noticed that the modem can drop out once every few days. Yes, the host is forced to reboot once a week for preventive purposes, but the modem’s interruptions can be sudden and frequent. At the moment, I use the standard SMS integration to check the modem’s status, specifically the change to “unavailable” of the operator’s name or signal level, but I’m thinking of abandoning this integration altogether.

Instead of a binary sensor, I think that's better to implement a service. Or a sensor representing the signal level but autoupdate must be disabled for such sensor. The sensor should be updated on demand using homeassistant.update_entity.

Feel free to create a patch for this feature.

[black-roland]

As a workaround, the similar could be archived using the serial integration: https://www.home-assistant.io/integrations/serial/

If a modem is still connected and working, it should reply with OK to the AT command.