The Federal Emergency Management Agency (FEMA) and Federal Communications Commission (FCC) plan tested an emergency alert system on October 3, 2018.
The test is meant to check the government's ability to distribute information in case of emergencies. This was the first mandatory national Presidential-level test.
FEMA said, "that some cell phones will not receive the test message." If you didn't receive one, it's probably because your wireless provider was not one of the Wireless Emergency Alerts (WEA) participants.
The test message was sent at 11:18 a.m. PST for mobile devices and 11:20 a.m. PST for other devices.
During the 30 minute cell tower broadcast, FEMA said, "WEA compatible cell phones that are switched on, within range of an active cell tower, and whose wireless provider participates in WEA should be capable of receiving the test message."
For frequently asked questions about the WEA visit FEMA's link.