||This paper describes the development of a public emergency messaging system in Western Australia. A set of design criteria were identified by a review of relevant published literature, a survey of current practice in Australia, and consultation with local stakeholders. The system should support: Multiple Recipients, Multiple Channels, Multiple Hazards, Multiple Stakeholders, Multiple Senders, Multiple Platforms, and Write Once Message Composition. A prototype system was built according to these design criteria, based on the Common Alerting Protocol version 1.0. The design was validated in trials simulating messages sent during a tropical cyclone and a bushfire. A total of 56 trial participants from identified stakeholder groups were surveyed with regard to their experience of the prototype system. Overall, the prototype system functioned successfully and participants reported high levels of satisfaction. The paper describes this research project and the initial stages of the subsequent development of a production system, called APECS.