Screenshot of flash flood warning from the National WEather Service on May 27, 2014.
Screenshot of flash flood warning from the National WEather Service on May 27, 2014.

On Tuesday night, residents in Eastern Massachusetts may have jumped at the sound of loud pulsing and vibrating coming from their cellphones, as a flash flood warning was issued by the National Weather Service. This was all part of a nationwide text emergency alert system called Wireless Emergency Alerts, which sends alerts to your mobile device in case of an emergency.

Here is a look at how the wireless emergency alert system works:

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What are these emergency cellphone alerts?

The cellphone alerts are part of the Wireless Emergency Alerts program (WEA), which is a national public safety system that allows authorized government agencies to send alerts to your mobile device. The program was established under the Warning, Alert and Response Network (WARN) Act, which was passed in 2006. The alerts come through with a vibration and tone, similar to the emergency warnings you may hear on radio and television.

Who sends out emergency alerts?

Alerts may be sent by the National Weather Service, the Federal Emergency Management Agency (FEMA), the Federal Communications Commission (FCC), the Department of Homeland Security, and local and state public safety agencies.

What type of alerts are sent out sent?

There are a variety of alerts that can be sent to your phone, but in general most alerts will be for extreme weather conditions, AMBER alerts, local emergencies requiring immediate action or evacuation, or presidential alerts during a national emergency.

Weather-related alerts are mostly sent for “more rapidly evolving and immediately life-threatening scenarios” such as flash floods and tornados, meteorologist Matt Doody of the National Weather Service in Taunton said. Warnings for tsunamis, hurricanes, and extreme wind may also be issued as alerts, according to the National Oceanic and Atmospheric Administration’s website.

In Massachusetts, AMBER alerts are officially issued by the State Police, who put it into an electronic system that goes to the National Center for Missing and Exploited Children, who are then able to issue a wireless alert for the state, Preparedness Coordinator Chris Besse of the Massachusetts Emergency Management Agency said.

Besse said MEMA also has the ability to send wireless alerts, and would do so for anything that requires the public to take immediate action. MEMA has only ever sent one wireless alert and that was a “shelter in place” warning during the Boston Marathon manhunt on April 19, 2013, Besse said.

How do the alerts get sent to cellphones?

The wireless industry is also a part of the WEA program along with the FCC and FEMA.

According to the FCC, participating wireless carriers (which were required to implement WEA in April 2012) send the alerts only from cell phone towers to mobile devices in the affected area. So, those who own WEA-enabled cell phones would receive geographically-targeted, text-like messages alerting them of imminent threats in their area. That means if you live in Boston, but are out of town in New York and there is an alert in eastern Massachusetts, you would not get the alert.

Doody said most new phones are capable, but not all phones are since it depends on the carrier. The WEA technology is becoming standard on new phones and all cellphone carriers are participating in the program in some capacity, Besse said. According to CTIA, a trade group that represents wireless companies, mobile users are not charged for the emergency alerts.