AusAlert:Overview National Test vs Emergency Alert Developer Gap CAP-AU Architecture All Systems GuideCAP-AU Guide | API Docs

What is CAP-AU?

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.

How AusAlert Uses CAP

AusAlert uses CAP internally to standardise alert messages before they are sent via cell broadcast. The flow works like this:

An emergency agency (CFS, RFS, CFA, etc.) decides to issue a warning
The alert is composed in CAP format with severity, urgency, certainty, geographic area, and message text
The Cell Broadcast Centre (CBC) receives the CAP message
The CBC converts it to cell broadcast format (limited to ~1,395 characters across 15 pages)
Mobile towers in the target area broadcast the message on dedicated signalling channels
Every compatible device in range receives the alert simultaneously

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.

Cell Broadcast Architecture

Emergency Agency (CFS, RFS, etc.)
    |
    v
CAP-AU Message (XML)
    |
    v
Cell Broadcast Centre (CBC)
    |
    v
4G/5G Mobility Management (separate signalling channel)
    |
    v
Mobile Towers (targeted by WGS84 coordinates)
    |
    v
All Compatible Devices in Range
    |
    v
Device GPS checks: "Am I in the target area?"
    |
    Yes --> Display alert, play siren
    No  --> Silently discard

Cell broadcast uses a one-to-many architecture. One message from the tower reaches every device. No phone numbers, no subscriber data, no network congestion.

CAP-AU Message Structure

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.

Device Standards

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's CAP-AU Output

EmergencyAPI produces validated CAP-AU output via the ?format=cap-au query parameter. Our CAP-AU output has been externally validated with 0 errors using cap-validator.appspot.com with the AU Profile checkbox enabled.

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 compliant emergency data.