I'm surprised the discussion here hasn't veered toward what actually happened. Technical glitch/human error? Hacked emergency alert system? Missile actually was on the way, but being a cheap North Korean one, it fell into the ocean on the way?

There are lots of potential explanations...whatever happened, there is stuff to work on in the aftermath of this. Barring the idea that it was an actual missile that failed to hit its target, if these alert systems are vulnerable, that's a bad thing. This could have caused serious chaos in a large city like New York. Techniques like this could be used to cause gridlock before a terrorist attack, suppress voter turnout on election days, etc.