CAP-AU is the Common Alerting Protocol, Australian Profile. It is an XML standard for formatting emergency alert messages, based on the international OASIS CAP v1.2 specification used by over 200 countries.
The Bureau of Meteorology (BOM) is the custodian of CAP-AU. The current version is CAP-AU-STD v3.0, published in September 2013. It was developed by a working group including Emergency Management Australia, Geoscience Australia, and state government agencies.
CAP-AU adds Australian-specific extensions to the base standard: event code mappings aligned with the AUeventLIST, geocoding using G-NAF and GDA94 references, and response type patterns specific to the Australian Warning System.
AusAlert uses CAP internally to standardise alert messages before they are sent via cell broadcast. The flow works like this:
The CAP message itself is not delivered to phones. Phones receive a condensed cell broadcast message derived from the CAP content. The full CAP record stays within the government system.
Emergency Agency (CFS, RFS, etc.)
|
v
CAP-AU Message (XML)
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v
Cell Broadcast Centre (CBC)
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v
4G/5G Mobility Management (separate signalling channel)
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v
Mobile Towers (targeted by WGS84 coordinates)
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v
All Compatible Devices in Range
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v
Device GPS checks: "Am I in the target area?"
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Yes --> Display alert, play siren
No --> Silently discardCell broadcast uses a one-to-many architecture. One message from the tower reaches every device. No phone numbers, no subscriber data, no network congestion.
A CAP-AU alert has three main layers:
| Element | Key Fields | Purpose |
|---|---|---|
| <alert> | identifier, sender, sent, status, msgType, scope | Message envelope: who sent it, when, and whether it is Actual/Test/Cancel |
| <info> | category, event, severity, urgency, certainty, headline, description | Alert content: what happened, how serious, what to do |
| <area> | areaDesc, polygon, circle, geocode | Geographic targeting: where the threat is, polygon or circle boundaries |
For a deeper look at the CAP-AU format with code examples, see our CAP-AU Developer Guide.
Communications Alliance published standard AS/CA S042:2025 for cell broadcast device compatibility. From 30 June 2026, all relevant devices imported into Australia must comply.
Two alert levels with different device behaviour:
| Alert Type | User Can Disable? | Override Silent/DND? | Use Case |
|---|---|---|---|
| Critical | No | Yes (siren, vibrate, full screen) | Imminent threat to life |
| Priority | Yes (via phone settings) | No | Watch-and-act, advice |
About 90% of Australian phones are compatible. iPhones from iOS 15.6.1+, Android phones from Android 11+. iPads are not supported.
EmergencyAPI publishes CAP-AU the way CAP was designed to be distributed: a standards-validated Atom feed at ?format=cap-atom, where each entry inlines a full CAP-AU <alert>, plus per-incident documents at /incidents/[id]?format=cap-au. Both validate against the OASIS CAP 1.2 schema and the CAP-AU Profile v3.0, confirmed with the Google CAP Validator.
The older ?format=cap-au list output wrapped multiple alerts in a non-standard element and did not validate as a whole. It is kept for backward compatibility but deprecated; new integrations should use the Atom feed.
While AusAlert uses CAP internally but doesn't expose it to developers, EmergencyAPI makes CAP-AU accessible. You can consume incident data in CAP-AU format for integration with emergency management systems, or use GeoJSON/CSV for mapping and analysis.
For implementation details, see the CAP-AU Developer Guide.
Build with CAP-AU formatted emergency data.