But the best-case scenario is that no emergency ever happens that's serious enough to warrant a nationwide phone alert.
It will be the first national WEA test, and the fourth nationwide test of EAS, the statement said.
The WEA test starts at 11:18AM local time on Wednesday, October 3rd, 2018.
Every smartphone in America received a Presidential Alert at 2.18pm.
The alternative is to buy a phone which isn't WEA-compatible, but most newer wireless phones are. The agency is coordinating with the FCC to test out this system.
The message will say: "THIS IS A TEST of the National Wireless Emergency Alert System".More news: Brexit negotiator Guy Verhofstadt mocks Boris Johnson's bridge plan
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The intent of the alert was to test the ability to warn Americans about a disaster, such as severe weather, or an event of national outcome. "No action is needed", the full text will read. Who Will Get the WEA Test?
Cell towers will also only broadcast the alert for about 30 minutes, so if you're on the phone or out of range for a half hour after 2:18 p.m. ET, you might miss it. That includes iPhone and Android OS phones.
There was no way to opt out of the test.
But with people unable to opt out, the hashtag #PresidentialAlert became the top trending topic in the USA on Twitter as people complained and joked about it.
The Department of Homeland Security posted a reminder about the test on Twitter on Tuesday, and reassured phone users that their numbers are not being shared with anyone. Some cell phones will receive the message; others will not.
People have the ability to opt out of other types of regional alerts - such as AMBER alerts for missing children or alerts related to weather warnings - through the settings on their wireless devices. Personal messages, campaign messages, and other political messages aren't permitted.
The presidential alert can only be activated by the current president, but the reasons for doing so are legally defined. The alerts are broadcast by FEMA, and must meet Integrated Public Alert and Warning System Modernization Act requirements before they can be broadcast.