When you get an alert, your phone will make a sound somewhat akin to the EAS warnings you hear on the radio or television from time to time, accompanied by a unique vibration. If you have your sound turned off, you should just get the vibration. The sound and vibration will be accompanied by an alert icon and a text message of up to 90 characters.
The text includes information such as alert category, time of the emergency and when it will expire, issuing agency, what the emergency is, who is affected and possibly a recommendation on how you should respond (such as seek shelter or evacuate). Amber alerts might include details about the abductor's vehicle including the license plate number. The message will repeat twice, and you may receive subsequent updates with new details. For more information, you can check for news of the emergency via other media such as TV, radio or the Web.
Participation by wireless carriers is voluntary, but more than 100 providers, including all the major ones, are already distributing the alerts. Participating carriers include AT&T, Bluegrass Cellular, Cellcom, Cricket, Sprint Nextel Corporation, T-Mobile USA, U.S. Cellular and Verizon Wireless among many others, and more carriers will be adding the service soon. Even most prepaid providers offer it. In some cases, carriers may only be providing the alerts on portions of their networks or to select devices. And not all devices are capable of receiving the messages.
The devices that can currently receive the messages are mainly newer smartphones and souped-up cell phones sometimes called feature phones. New phones that have this ability bear a CTIA Wireless Emergency Alerts Capable logo. Your older device might be able to get them after a software upgrade, or it might be entirely incompatible. If you aren't sure, your carrier should be able to tell you whether your device can receive the alerts.
There is no need to subscribe to the service. If you have a WEA-enabled phone, you are automatically enrolled to receive the messages. You are not charged anything and they do not affect your text message limits or voice and data usage.
The alerts are geographically targeted and designed to go out to the county or counties where an emergency is occurring, but they can be sent to entire states, the entire nation, or possibly even smaller areas than counties under certain circumstances.
Cell phones have had the ability to receive Amber alerts since 2005 through an SMS text message based program called the Wireless Amber Alert program. It was an opt-in service that around 700,000 people signed up for, and which sent messages only for alerts in geographical areas picked by the users via traditional SMS [sources: Hu, CTIA, U.S. DoJ]. It was shut down in favor of the WEA system on December 31, 2012. WEA uses a different technology entirely.