Washington (CNN) The "presidential alert" headed to Americans' cell phones won't actually be written by President Donald Trump, the Federal Emergency Management Agency said Tuesday. 
 
 Wednesday afternoon's message is the first nationwide test of the system built by the government and cell phone carriers to push an emergency message to nearly all cell phones in the US, a senior FEMA official told reporters on a Tuesday conference call. 
 
 Despite the name, "the president will not originate this alert, say, from his mobile device," the official said. "You would not have a situation where any sitting president would wake up one morning and attempt to send a particular message." 
 
 That name had generated questions about how and when the system can be used. The official said the uses are limited, such as to a "coordinated attack on our major cities across the country" or "some other type of public peril that is ongoing in the country at the time." 
 
 The FEMA official spoke to reporters on a conference call the agency arranged on the condition of anonymity. FEMA did not elaborate on why the official could not be named. 
 
 Read More ||||| WASHINGTON (Reuters) - The Trump administration will send messages to more than 200 million U.S. cellphones on Wednesday testing a previously unused presidential alert system that aims to warn the public in the event of a national emergency. 
 
 U.S. President Donald Trump rallies supporters during a Make America Great Again rally in Southaven, Mississippi, U.S. October 2, 2018. REUTERS/Jonathan Ernst 
 
 The test message was originally scheduled for September but was pushed back to Wednesday at 2:18 p.m. EDT. 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.. 
 
 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 (VZ.N) 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 U.S. 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. ||||| Editor's Note: The presidential test alert was successfully sent Wednesday, Oct. 3. Read the latest story here . 
 
 It's the alert that – if it's real – you won't want to get again. For the first time ever Wednesday, Americans nationwide will receive an alert on their cellphones from President Trump. The test, scheduled for 2:18 p.m. ET, is the first test of a national presidential alert system that will let any president issue a warning about a crisis. That could include a missile launched by another country at the U.S. or a tsunami. 
 
 First on "CBS This Morning," we got an inside look at the new system with Federal Emergency Management Agency (FEMA) officials ahead of the test. 
 
 "When those messages appear on mobile devices, people should take those extremely seriously," FEMA's Antwane Johnson told CBS News correspondent Anna Werner. "It has some direct impact on either life or safety." 
 
 Johnson directs the agency's public alert warning system that will send out the nationwide test of the presidential alert Wednesday. 
 
 
 
 "If we have something that's of national significance, we can rapidly notify the American public of that event," Johnson said. 
 
 Government agencies nationwide have issued more than 40,000 emergency alerts to cellphones since 2012. But those Amber and weather alerts target specific regions. This new presidential alert will be nationwide and only used for advance warning of national crises. 
 
 "It should be reserved for true situations, true emergencies when we need to get the public's attention," former Secretary of Homeland Security Jeh Johnson said, adding it is designed to be used very specifically – and rarely. 
 
 "This is something that should not be used for a political agenda," Jeh Johnson said. That's especially important because no one can opt out of these alerts, he said. 
 
 "Now you know you say presidential alert and some people are thinking, 'Aw man, I see President Trump sending out Twitter messages all day long. Does this mean I'm going to get whatever message President Trump wants to send out through this alert system now?'" Werner said. 
 
 "No, not at all. One thing that we need make very clear is that there are laws, policies and procedures that are in place, other protocols to assure that the system is used in accordance with its intended use as defined by the law," Johnson responded. 
 
 
 
 Alerts are not foolproof however. In January, Hawaii's emergency management agency mistakenly sent out an alert warning of a ballistic missile threat to more than a million cellphones. Mistakes like that could make people nervous about this new nationwide alert. 
 
 "The fact that you can't turn this alert off, that it will be something that will arrive on your phone whether you like it or not, I think was perhaps upsetting and concerning to some people," said Andy Whitehouse, who teaches communications at Columbia University. 
 
 Three New Yorkers filed a federal lawsuit last week attempting to block the test, saying it violates free speech and is an unconstitutional seizure of electronic devices. The test will set off the same loud sound used for other alerts. If your cell is on and you have service, you will likely receive it and cannot stop it.
– A text message from President Trump will be sent to more than 200 million US cellphones in a test starting at 2:18pm Eastern on Wednesday—but officials stress that the president won't be texting Americans on a regular basis. The Federal Emergency Management Agency says the "Presidential Alert" message is a test of a new alert system for national emergencies, reports Reuters. "THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed," the message will read, according to FEMA, which says the alert will have a loud tone and a "special vibration." A senior FEMA official said Tuesday that the message will not be coming from Trump's phone and use of the system will be restricted to events like major attacks on US cities or "some other type of public peril," CNN reports. "The president will not originate this alert, say, from his mobile device," the official said. "You would not have a situation where any sitting president would wake up one morning and attempt to send a particular message." Former Secretary of Homeland Security Jeh Johnson tells CBS that the system is definitely "not something that should be used for a political agenda"—especially since there is no way for Americans to opt out of receiving the alerts. The test was originally scheduled for Sept. 20, but it was postponed due to Hurricane Florence.