---
title: "Prove that alerts still reach you · Agent Wranglers"
url: https://agentwranglers.se/playbook/operations/alerts-and-on-call/alert-pipeline-heartbeat
updated: 2026-10-20
licence: "All rights reserved"
---

# Prove that alerts still reach you

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Required
- Chapter: [Alerts and on-call](https://agentwranglers.se/playbook/operations/alerts-and-on-call)
- Rule: Keep one alert that always fires and goes to an outside service, which pages when it stops arriving. Send a test page every month.
- How: A stopped alert manager, an expired paging key or a broken mail relay fails silently, and then every other alert is silent too. Prometheus setups call this always-firing alert Watchdog. Route it to a heartbeat monitor outside your own systems that expects it every few minutes. Once a month, send a test page and confirm the on-call phone rings.
- Check: Stop the alert manager on staging. The outside monitor pages within 15 minutes. The paging tool shows a test page from the last 31 days.

Example:

```yaml
# Prometheus rule: always firing
- alert: Watchdog
  expr: vector(1)
  labels:
    severity: heartbeat

# Alertmanager: repeat it to the outside monitor every minute
route:
  routes:
    - matchers: ['severity="heartbeat"']
      receiver: outside-heartbeat
      group_wait: 0s
      group_interval: 1m
      repeat_interval: 1m
receivers:
  - name: outside-heartbeat
    webhook_configs:
      - url: https://heartbeat.example.com/ping/alerting
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers operations playbook: https://agentwranglers.se/playbook/operations/alerts-and-on-call/alert-pipeline-heartbeat`.

- Previous: [Alert when a scheduled job stops running](https://agentwranglers.se/playbook/operations/alerts-and-on-call/job-heartbeats)
- [Alerts and on-call](https://agentwranglers.se/playbook/operations/alerts-and-on-call)