The Trump administration will send messages to more than 200 million US cellphones on Wednesday testing a previously unused presidential alert system that aims to warn the public in the event of a national emergency.
The test message was originally scheduled for September but was pushed back to Wednesday at 2:18 p.m. EDT (1818 GMT). The Federal Emergency Management Agency (FEMA), which will send the alert, said the messages would bear the headline "Presidential Alert," and that phones will make a loud tone and have a special vibration.
The test has been scheduled to ensure that the alert system would work in the event of a national emergency. The message will read: "THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed." A separate alert on TV and radios will be issued at 2:20 p.m. (1820 GMT)
The tests have drawn a lot of attention on social media in part because of President Donald Trump's propensity for sending tweets to his 55 million followers.
On a conference call, government officials told reporters that Trump would not personally trigger the alert -- from his phone or any other device -- and emphasized that no president could "wake up one morning and attempt to send a personal message."
The test alert will be sent by a device similar to a laptop from a FEMA laboratory.
An actual alert would be used for an impending missile attack or other national emergency.
Then-President Barack Obama signed a law in 2016 requiring FEMA to create a system allowing the president to send cellphone alerts regarding public safety emergencies.
Federal Communications Commissioner Mike O'Rielly told reporters on Tuesday that an April 5 regional test of the emergency alert system in the Washington area showed some potential issues.
He said some people did not receive alerts on some devices during that test. "We're trying to analyze that," O'Rielly said.
The country's wireless emergency alert system has issued over 36,000 alerts for situations such as missing children, extreme weather and natural disasters since 2012, but never a presidential directive.
Cellphone users can opt out of natural disaster or missing children alerts, but not presidential alerts. Verizon Communications Inc said nearly all of its mobile phone handsets are capable of getting alerts.
Government officials estimated that the alert would reach upwards of 225 million US cellphones, or around 75 percent of all phones. They said a person on a call lasting 30 minutes may not get the alert as with phones with an active data connection.