FEMA will conduct the first nationwide test of its Wireless Emergency Alert system today beginning at 2:18 PM Eastern. While you can choose to opt out of mobile weather and AMBER alerts, you won't be able to opt out of this test. When it happens, you'll see a notification on your phone with the header "Presidential Alert" and the message will say, "THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed." Cell towers will broadcast the test for 30 minutes and any compatible phone that's on, within range of an active cell tower and connected to a wireless provider participating in WEA will receive the message.