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If there had been a national activation of the Emergency Alert System around 9:42 AM EST on 9/11 (when American airspace was closed by the FAA), this would have activated the before work and possibly school for about half the country, and television coverage would have been replaced with text and audio messages, with no video or images. It would also be less than ten years since the end of the Cold War, when a national level activation would have meant bombers and missiles were incoming, and it's on a Tuesday morning, when tests don't occur.
What's the impact of the activation under these circumstances?