> This is a watchdog timer / monitor / heartbeat, setting off an alert if a timer elapses.

Notice from the config file, this doesn't actually do checks, only has passive listeners with a remote switch to toggle. That makes this a dead man's switch, not a watchdog / angel / monitor / heartbeat check.

This doesn't do anything except sit there watching a clock not knowing if you're dead.

The service you want monitored, the service you want to be sure the heart is beating, has to ping this to demonstrate aliveness.

If this doesn't get a ping in time, it then acts by telling pagerduty to alert.

If your service (man) is dead (or your service otherwise can't reach this to check in in time), this switches PD to alert mode.

So, dead man's switch does seem a fair characterization.