The alert test, which is FEMA's first for the wireless emergency system - and is being coordinated with the Federal Communications Commission - will sound similar to an Amber Alert or flood watch warning.
Two minutes later, the EAS test takes place - this is the system used by the President to send out messages during national emergencies via radio, television and other platforms.
"The nationwide test ensures that in times of an emergency or disaster, public safety officials have methods and systems that will deliver urgent alerts and warnings to the public", said OEM. "No action is needed", officials said.
"The test is meant to ensure public safety officials have the methods and systems to deliver urgent warnings and alerts to the public in times of an emergency or disaster", said Acting IEMA Director William Robertson.
The system is used to warn the public about unsafe weather, missing children and other critical situations while also providing the president the capability to address the nation during a national emergency.
The test message was originally scheduled for September but was pushed back to Wednesday at 2:18 PM EDT (2318 hours, Pakistan time). Users connected to a participating wireless network and within range of an active cell tower, will receive a text message. That can include radio and television, and in this case, cell phone services.
The Wireless Emergency Alerts (WEA) system proper was created in 2012, but it's actually been around longer than that. Others will not. No action is required.
Don't be surprised if you get a text around 1:18 p.m. Wednesday from President Donald Trump's office. You'll know you've gotten the message if the header reads "Presidential Alert".
Sorry, but you can't opt out of receiving this alert (nor can you silence it on your phone unless you set the device in "Do Not Disturb" mode, which varies by phone model).
Cell phones should only receive the message once.
This new presidential alert will be nationwide and only used for advance warning of national crises.
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 WEA and EAS systems are used to warn the public about emergencies, such as unsafe weather or missing children, according to FEMA.