Today, October 3rd the Federal Emergency Management Agency AKA FEMA will conduct an emergency text message alert. They're test the capabilities of the integrated Public Alert and Warning system known as IPAWS. The test happens at approximately 2:18 pm today. The test is done in coordination with the FCC. This is the 4th test of the system since 2011.
The test will be broadcast for about 30 minutes to compatible cell phones that are switched on and within range of an active cell tower. Some phones will not recieve the test and phones should only recieve the test once.
The test alert will have a header that reads "Presidential Alert" followed by text that says:
“THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed.”
This page on the FEMA website has all the details and FAQ you might want about this alert