Put a dead man's switch on every cron job you care about
20 checks, no card.
Cron will start the command. It will not tell you the command never ran because the machine was off, the crontab was overwritten, or MAILTO went into a black hole. A dead man's switch is the missing signal: expected ping did not arrive.
A minimal crontab line
0 2 * * * /usr/local/bin/backup.sh && curl -fsS -m 10 --retry 5 https://www.pingclock.com/ping/YOUR_ID
The && is the whole trick. If backup.sh exits non-zero, the ping does not fire, and the check goes down after grace.
Grace
If the dump usually takes 12 minutes, do not set grace at 2 minutes. You will page yourself on a slow night. Forty-five minutes is a common backup grace. Five minutes is fine for a job that always finishes in 30 seconds.
Time zones
Write the check in the same zone as the crontab. "0 2 * * *" in UTC is not 2am in Chicago. If you change servers across a DST boundary, prefer a named zone on the check, not a hand-shifted hour.
FAQ
What if the ping URL leaks in a log?
Treat it like a secret. Anyone with the URL can keep a dead job looking healthy. Rotate the check if it was pasted in a ticket.
Can Windows Task Scheduler do this?
Yes. Add a curl or Invoke-WebRequest step at the end of the task, same as cron.