We would know When and where they could be denonated . The device has to be lined up with the sun and the position on earth and be detonated at that moment. Theres a small window of oppertunity of when and where this could be done.

Imagine if they were to release a calender of when and where locations for possible detonations are possible for the public to review.The people would panic every time that window lined up over there heads.