iPhone 5 supports Wireless Emergency Alerts. The alerts are on by default. You can find the WEA settings by going to the phone settings, and scrolling down to the bottom. WEA is called Government Alerts on the iphone.
There are a couple of reasons a device could receive what is perceived to be duplicate messages.
First, if you receive a WEA message and then delete it before the alert expiration, the device will have no record that the message had been received previously and will display the alert again when the network rebroadcasts the message (this is done at a regular interval). To keep this from occurring, when a WEA message is received do not delete the message until after the expiration time stamp included in the message. As long as the message stays in the inbox, the device will know the message has already been alerted and will not display the alert again (or provide notification).
Second, if the message originator sends mulitple messages that have the same text and happen to have overlapping target areas, the device will receive and display multiple alerts because they are distinct different messages with different message ids. Should this occur, feel free to provide feedback as we are working to help FEMA and the message originators create/modify processes and tactics to ensure full coverage of emergency information while keeping customer intrusion to a minimum.
The Department of Homeland Security's Science and Technology Directorate will be hosting the CMAS Forum at the International Wireless Communications Expo on February 21, 2012.
This forum will bring together stakeholders from all levels of government and the wireless industry to discuss the rollout of CMAS, and ensure that alerts and warnings stakeholders have all the information and tools necessary to integrate CMAS into their existing alerts and warnings systems.
Please refer to the attached documents for further information.
Sprint in cooperation with FEMA, the NYC Office of Emergency Management, and other wireless carriers will be conducting a series of tests on December 15th to prepare NYC OEM to start sending emergency messages via the WEA/CMAS system at the beginning of 2012.
Tests will be conducted throughout the 5 boroughs and will be received by any CMAS capable device that has had the software activated.
If you receive one of these test messages, there is no action to take, this is only an exercise to ensure the system is ready from NYC OEM's perspective so that they are able to push forward with their production implementation.