My setup is “simple” and all these monitoring functions are performed in my opnsense box with the telegram plugin.

Most of the alerts are pretty basic and are done into the FW level or the outbound basic logging. So opnsense with the basic tooling is just enough.

I have in my todo to connect the logging system from opnsense to a proper Prometheus/grafana system to really have proper log of several days without having an impact on the FW but I never find the time to do it (lazyness problem)