By that thought process, wouldn't these people more likely to have their hidden phone discovered by spontaneous Amber Alerts? Those come with no warning, whereas the NAS did come with a heads up.

It's not relevant to me, i'm in a different country, but in i've seen daily completely turn off your hidden phones, and only turn them on when it is safe because the alert will still blare when you turn on you phone the entire week before the test and also months before. Certain circles take warning each other about 'Loud Day' seriously.