Federal officials are planning to do the first nationwide test of the broadcast Emergency Alert System. FCC rules now provide for voluntary testing at the state and the local level, but not nationally. The FCC has issued a Second Further Notice of Proposed Rulemaking to change the rules governing the Emergency Alert System to conduct national testing at least once a year.
To the best of my knowledge there has only been one other national test of this system, and that was more than sixty years ago, when it was known as CONELRAD. The radio part of it involved swapping out transmitter crystals to make every radio station in America transmit on either 640 or 1240 kHz, in order to confuse what were then sophisticated enemy missile guidance systems. No film, video or audio tape of the test is known to have survived the years.
By the 1970's it had become the Emergency Broadcast System and one Saturday morning in 1971 some guy at Cheyenne Mountain loaded the wrong tape into the system.
There is no reason to believe that another national test will do any less than wreak similar havoc.
UPDATE: Jay Philpott has provided what he claims to be the audio for the oldest CONELRAD test, including Groucho Marx' suggestions to citizens, from a Buffalo NY
