Metrics

A monitoring system can collect the state of the wall: Settings > Metrics makes a token, and from then on GET /metrics answers whoever sends it, in the text format that Prometheus and everything that reads its format understand:

scrape_configs:
  - job_name: qkvm
    metrics_path: /metrics
    authorization:
      credentials: qkvm_...            # the token, as shown once when it was made
    static_configs:
      - targets: ["192.168.1.20:8787"]

qKVM answers when it is called by an IP address, by a name without a dot, or by one ending in .local, .lan, .internal, .home.arpa or .ts.net. Any other name the collector is to reach it by has to be listed under allowed_hosts, as for a browser; use the offline server settings command.

Metric	Says
`qkvm_devices{state}`	how many tiles are in each state: `online`, `no_signal`, `offline`, `auth`, `error`, `busy`, `connecting`
`qkvm_device_up{id,device,kind,group}`	1 while that device answers, 0 while it does not
`qkvm_device_picture{...}`	1 while it shows a picture; for a server, while it is switched on
`qkvm_device_last_seen_seconds{...}`	seconds since it last answered
`qkvm_device_temperature_celsius{...,sensor}`	how warm it is: the KVM itself (`sensor="device"`), or each sensor of a server
`qkvm_server_healthy{...}`	1 while a server's management controller calls it healthy
`qkvm_unlocked`	1 while qKVM can talk to its devices (somebody has signed in since it started)
`qkvm_sessions`, `qkvm_devices_configured`, `qkvm_update_available`, `qkvm_info{version}`, `qkvm_start_time_seconds`	about qKVM itself

The token is shown once and qKVM keeps only its hash. It lets its holder read the above and nothing else; a new one replaces it, and Switch off makes /metrics answer nobody.
While metrics are on, qKVM goes on watching the devices after the last person has signed out, as it does for alerts: the saved device passwords stay usable in memory for that.
After a restart qKVM goes on by itself. Started with --locked-start (see Keeping it running), nothing can be collected about the devices until somebody signs in; qkvm_unlocked is 0 until then, which is worth an alert of its own.
A collector is nobody watching: a JetKVM that is not on screen is only asked whether it answers, as for alerts, and its one viewer is left to whoever wants it.
GET /healthz is separate and needs no token. It says that qKVM is running, which version, and whether it is still waiting for a sign-in after a restart ("locked").