By the end of this month, the major mobile operators in the US, which cover about 97 percent of the population, will support wireless emergency alerts from federal, state, local, and tribal government agencies about imminent threats to safety, including severe weather events and missing children. The messages, also called the Commercial Mobile Alert System (CMAS) and Personalized Localized Alerting Network (PLAN), will appear similar to text messages but they will not cost anything or count against the receiver's text plan. The messages are an additional method for getting the word out about emergencies and aim to be a supplement to the existing Emergency Alert System, which runs messages over radio and television.

The FCC and FEMA (Federal Emergency Management Agency) teamed up with US mobile carriers to create the supplemental service.

Only public safety entities can issue the alerts, which fall into three categories: Presidential Alerts, which are issued by the President of the United States or a designee. Imminent Threat Alerts, which include severe man-made or natural disasters, such as hurricanes, earthquakes, tornadoes, etc. AMBER Alerts, which meet the U.S. Department of Justice's criteria to help law enforcement search for and locate an abducted child. While consumers can opt out of Imminent Threat alerts and AMBER alerts, they cannot opt-out of Presidential Alerts.

The alerts are location-specific and will be sent to people who have "WEA-capable" devices in the affected areas. Even if a consumer has a Massachusetts phone number, for example, and is visiting California, he will receive a message if an earthquake occurred while he was visiting the affected area of that state.

Interestingly, the alerts will have a "unique audible signal and vibration cadence to emphasize its important," according the wireless association CTIA's FAQ on the program. The messages will be no more than 90 characters in length, and include: an alert icon, info on who is sending the alert, what is happening, who is affected, and what action to take.