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Fallback Numbers

Configure a secondary phone number to use when the primary SMS or voice call fails to deliver.

What is a fallback number?

A fallback number is a secondary phone number that AlertFlow tries when the primary number for an SMS or voice call fails. This handles scenarios like:

  • The engineer's phone is off or out of service
  • The primary number is a VoIP line that doesn't accept SMS
  • Twilio fails to deliver to the primary number after retries

How fallback works

When a Notify node sends an SMS or voice call:

  1. AlertFlow attempts delivery to the primary phone number
  2. If the delivery fails (Twilio error, undeliverable, timeout), AlertFlow waits 30 seconds and tries the fallback number
  3. Both attempts are logged in the notification log with their respective status

The fallback only triggers on hard failure — not if the engineer simply doesn't reply.

Setting a fallback number

Fallback numbers are set per team member:

  1. Go to Settings → Team Members.
  2. Click the team member you want to configure.
  3. Under Phone, fill in the primary number.
  4. Under Fallback Phone, fill in the secondary number (e.g., a desk phone, spouse's cell, or manager's number).
  5. Click Save.

Both numbers must be in E.164 format: +15551234567.

Per-workflow fallback override

If you want a workflow to always use a specific fallback number regardless of team member settings, you can configure it in the Notify node:

  1. In the Notify node Inspector, expand Advanced.
  2. Toggle Override fallback number and enter the number.

This is useful for high-stakes workflows where you always want to reach a specific backup (e.g., the NOC line).

Fallback for on-call routing

When a Notify node targets the On-call engineer (rather than a specific person), AlertFlow uses the on-call engineer's own fallback number if their primary fails. If the on-call engineer has no fallback configured, AlertFlow logs the failure and continues to the next step in the workflow.

Monitoring fallback usage

Check Settings → Notification Log and filter by Status: failed to see cases where the primary number failed and the fallback was (or wasn't) used.

Warning

If both the primary and fallback numbers fail, AlertFlow logs the failure and continues the workflow execution — it does not retry indefinitely. Make sure escalation paths in your workflow continue to the next tier if a notify step could fail.

SMS vs. voice fallback

The fallback number is shared between SMS and voice. If the Notify node sends both (one SMS + one voice call in the same workflow step), each uses the same fallback number on failure.

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