Sandy Hook had recently installed a state-of-the-art security system where everyone needed to be buzzed in. So he went through a window... No security system is perfect, just like no answer to this thread is going to be.

Recently Michigan legistlation passed the "right to work" bill and there was a large amount of upheaval. Because of that, my employer released a statement with precautionary plans for different scenarios (bombs, shooters, etc) and most of it was "watch for thigns that seem odd, go with your gut, get out of there and call 911". We are not allowed to be armed at work, but are very much a part of the public and have angry visitors at times. Taking schools out of the debate, what do other work places do to prep for these situations?