What are Wireless Emergency Alerts and how do they work?

If you are a New York City resident with a smartphone, you most likely received the following notification on the morning of September 19^th :

The message, issued via the Wireless Emergency Alerts (WEA) system, was sent out to nearby cell-phone users as police began a search for the man believed to be connected to the bombings in Manhattan and New Jersey the previous weekend. For some, this may have been the first alert they had ever received. If you, too, are unfamiliar with the WEA system, here is what you should know about how it works:  

1. The WEA system was introduced in April 2012. Rarely used, it is implemented in only three cases: extreme weather (and other threatening emergencies) in your area, AMBER alerts, and presidential alerts during a national emergency. No more than 90 characters in length, a typical WEA will show the type and time of the alert, any action you should take, and the authorized government agency issuing the alert.  

2. WEAs are different from text messages, which transmit over a phone network and require the sender to know the phone number of the person they wish to reach. Because regular cell networks can overload during an emergency, the WEA system uses a technology called cell broadcast messaging. This enables alerts to bypass wireless traffic and reach anybody in range of a geographically-targeted cell tower.  

3. The Federal Emergency Management Agency (FEMA) manages an online tool called the Integrated Public Alert & Warning System, or IPAWS. Any of the hundreds of agencies authorized to send WEAs create an alert using IPAWS, which then passes the alert to phone carriers, who then deliver the alerts to your phone.  

4. Wireless carriers’ participation in the WEA system is voluntary. However, should they choose to participate, they have no say in whether or not a particular alert gets sent out. For most carriers, WEAs reach customers’ phones within minutes or even seconds, overriding the volume controls of your phone to chime a unique sound and vibration so that you know it isn’t just another text message or push notification.  

5. WEAs are supported on a device-by-device basis. While most devices these days are WEA-capable, an older smartphone may not have the necessary technology. If you have a WEA-capable phone, go here to learn how to make sure you are opted in to receive alerts (or, if you prefer, to opt out of receiving them). Note that you may only opt out of WEA messages for imminent threats and AMBER alerts — presidential messages will still come through.

Sources: FEMA, Washington Post, Mashable