Regarding active shooters, I think the biggest challenge is figuring out who is supposed to be there and who isn't. That is challenge enough in my building, but the neighboring buildings even more so. There was a bomb blast in the 2nd floor of my current building about 14 years ago that took the door off the hinges. It turned out to be the Coca Cola delivery guy. It missed one of the Naval officers by about a minute or less. The unsettling thing is that a spree shooter could be someone you know or recognize.