We've been doing this for years ever since teenagers have been arriving in our neighborhood for years in busses. Especially the teenagers that are adult sizes and either do not wear a costume or wear a costume where they have a weapon in hand.
Our security door is locked and usually my wife responds to the door bell or the sounds of little guys saying, "Trick or Treat." If she sees a suspicious person, she alerts me and if she handles the distribution of goodies she knows that if something goes down that she is to drop to the floor and I will try my best to draw and react to the situation. When she first alerts me, I stand to her left and three feet back.
There have been times that we refuse to open the security door and tell the "big" kids that we have run out of candy.
Other times, I handle the distribution of candy...hold the bucket with my left, right on gun butt..and tell the "big"kids, no more than three candies.
Have a safe and sane Halloween...
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