Glossary · Monitoring

Dead Man's Switch (Monitoring)

A dead man's switch alert fires when an expected signal stops arriving, such as a cron job that fails to check in or a monitoring pipeline gone silent.

Updated October 6, 2026

A dead man's switch in monitoring is an alert that triggers on absence. A job or system must regularly send a signal, and if no signal arrives within the expected time, the alert fires. The name comes from mechanical safety devices that act when an operator lets go.

Why it matters

Most alerts detect a bad event. They cannot detect that nothing happened, which is exactly how many failures look: a backup that never ran, a scheduler that stopped, an agent that crashed. Absence-based checks catch these silent failures. They are also used to verify that the alerting pipeline itself works, via an always-firing "watchdog" alert that must arrive at an external receiver.

Example

A nightly backup script pings a unique URL on success:

0 2 * * * /usr/local/bin/backup.sh && curl -fsS https://monitor.example.com/ping/abc123

If no ping arrives within 25 hours (24 plus a grace period), the monitor sends an alert.

Common mistakes

  • Pinging at the start of the job rather than after success, so failures look healthy.
  • A grace period too short for jobs with variable run time.
  • Forgetting to monitor new scheduled jobs.
  • Hosting the receiver on the same infrastructure being watched.

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