I think that a whole lot of these groups are going to alilate each other long before they reach us. That means that only the best of the best are going to reach us.
That means I need to play the evasion game and guerrilla tactics of knowing the area I am in.
I suspect they will size up our group pretty quick and either go get backup to take us on or leave us be.
In either case, we want to detect them by knowing the area, if someone was there, we should know and see the signs. We may not be there when they come back.
Did you ever read *One Second After*?
You might find it very useful in answering many of your questions and concerns.