FEMA and FCC will conduct a Nationwide Emergency Alert Test on August 11th at 2:20 p.m. Test messages will be sent to televisions and radios, along with select cell phones that have opted-in to receive test messages.
According to the notice, the test will be very similar to regular monthly tests typically originated by state authorities. During the test, radios and televisions across the country may interrupt normal programming to play the test message. The message may be delivered in English or Spanish.
More details can be found here.