I don't even open my door if I don't know who it is. I go to the window next to it and ask through the screen what they want.
One time years ago my doorbell rang. I was busy with my then baby so I didn't answer. After two rings, the guy tried to open the door. Pulled and yanked on the knob - probably assuming no one was home. It scared the snot out of me!
I learned later that two homes were robbed during the day in my neighborhood. Several people said they had seen a young man who just didn't "belong", but no one (including me) took the time to notify the police...
If I am working in the back yard, my front door is locked!