Whatever each tool's default screen shows, and nothing layered on top.
There isn't really an observability layer here. Each service has whatever UI it ships with, and that is mostly enough for me to spot when something has gone sideways. There's no Prometheus or InfluxDB or Grafana or anything custom layered on top. Home Assistant happens to put a few sensors I actually care about on its default screen (Pi temperature, UPS battery and load, air quality from the Aranet4, Zigbee battery levels), and the companion app pings me when an automation decides something is worth a buzz. Day-to-day this works. Year-over-year analysis would need a real metrics stack, and that one is genuinely overdue.