‘On Wednesday, October 4 in the U.S., the Federal Emergency Management Agency (FEMA) will test its Wireless Emergency Alerts (WEA) system. At 2:20 p.m. Eastern, people will receive a message on their mobile phones that reads, “THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed.” In addition to the message, your iPhone will vibrate and play “a special sound that’s similar to an alarm” even if your iPhone is on silent. The alert will appear in Spanish for users who set their devices for that language.

FEMA says that the test will run for 30 minutes, so if your phone is off at the start of the test but then turned on during the 30-minute window, you will get a test message. The test message should be sent only once and you can delete the message after it is received. If a person subscribes to a wireless provider that does not participate in WEA, they will not receive the test….’ (Macworld)