The Wireless Emergency Alerts that pop up on our mobile screens resemble the Short Message System (SMS) text messages that many of us are used to sending and receiving, but they are actually sent via a different method, in part to avoid network congestion-related delays that can sometimes hinder text and voice messages. They also don't use individual phone numbers or GPS to get to people in the areas affected by an emergency.
WEAs are instead sent out via a special cell broadcast wireless carrier channel from cell towers in the affected area. It is a point-to-multipoint system that sends messages to every WEA-capable phone within range of the towers of participating carriers in the entire geographical area designated by the creators of the message.
When you are traveling, you should receive alerts appropriate to your current location, not your area of residence, as long as you are roaming on a participating provider's network and have the right phone. It is, however, possible for two people in the same location to be on different towers, leading to one getting an alert and one not getting it. You may also get them for emergencies in nearby areas that you are not currently in since they are broadcast using a radio-like technology from cell towers and their range might go beyond county boundaries.
Alerts should not interrupt your phone conversations or data transfers. The messages will be rebroadcast at regular intervals while an emergency is going on, and in that way may display once you end the call or session. Because of the rebroadcasting, you should also get them when you wander into an affected area after the initial warning is sent but while the danger is still present.
WEA-capable phones should display an alert the first time it is received and reject any duplicates. If the alert repeats more than the prescribed two times, it is most likely that new alerts were issued with additional or slightly different information.
Despite fears to the contrary, there is no citizen tracking going on via this system. The messages are broadcast as a one-way communication out to all capable mobile devices in range of the broadcasting cellular towers. No information is collected from the phones.
All messages are initially sent from authorized federal, state and local authorities to FEMA's IPAWS system, which verifies, formats and routes the messages to multiple warning systems, including the Emergency Alert System (EAS), National Oceanic and Atmospheric Administration (NOAA) Weather Radio All Hazards (NWR) and Wireless Emergency Alerts (WEA) program, among others. Messages are authenticated and converted to the Common Alerting Protocol standardized format through IPAWS OPEN, an open platform for emergency networks. Alerts that are IPAWS compliant will be sent to all public alert systems.
EAS messages are sent as usual via AM, FM and satellite radio, and broadcast, cable and satellite TV. NOAA's NWR broadcasts all types of emergency alerts, not just weather related ones, at various frequencies in the VHF public service band, and the broadcasts can be picked up with special receivers. IPAWS OPEN can also distribute messages to existing telephone or e-mail alert services, voice sirens, digital road signs and other local emergency message delivery services.