My early warning systems are as follows: K9 whom thinks he is King Kong, motion detection lights and.....My hearing is real good. I am lucky enough to live in a lower crime area and have great neighbors that look out for me as I do for them. That said, I still find my day to day status in a low caution yellow mode. I have only armed myself a few times when answering the door. If I don't know who it is, I seldom would take the chance to open the door. If I do the dogs happy dental work is right beside me to show the visitor not to be frisky or he might leave his reproductive organs at the steps. I would sometimes go upstairs and open a window and talk down on the unknown visitor. It keeps them about 9-10' away from me and they have know idea that I have armed myself.... The K9 is one great weapon of deterence in my home.......Just love that Shep..... If I was living in a different area that was known for crime I would have a lot different tactics too...
Good luck and stay safe.....