A national alert test buzzed US TVs, radios, and any phones that opted-in at 2:20PM ET

FEMA conducted an emergency alert system (EAS) test at 2:20 PM ET. It covered radio, TV broadcasts and mobile devices in the US. However, you may not be able to see it on your smartphone. This is because unlike the Presidential Alert test of 2018, this test only reached phones that were set to receive test messages. By default, however, most phones can opt out.This PDF document (PDF) by the FCC states that Android phones should have a Wireless Emergency Alerts section under their settings menu. It will contain an option for State/Local test alerts, which you can turn on/off. Although the process for iOS is more complex, Apple's support page provides information on how to opt in:Open the Phone app, and tap Keypad. Turn it on by entering *5005*25371#. Tap the green phone icon. An alert will appear that states Test alerts enabled. Tap the green phone icon to turn it off. An alert will appear that Test alerts are disabled.Wireless handsets that have subscribed to the Wireless Emergency Alert (WEA), will be able to display this year's test messages. This will enable a nationwide test, without disturbing the public.Read more about opting in here: https://t.co/kvGqLyBCqy https://t.co/LW3UptMxK7 National Weather Service (@NWS) August 9, 2021This is the mobile message for those who missed it or weren't eager enough to sign up:This is a test of the National Wireless Emergency Alert system. There is no need to take any action.Update at 2:30 PM ET: This update was made to reflect the fact that the test took place.