Having a gun in the home is certainly normal. In fact, not having a gun in the home and living in any number of "bad neighborhoods" would be abnormal.
What I suggested was that certain "abnormal" people might well lie in wait for the unwary innocent person to foolishly ring the doorbell.
Maybe, there are all kinds out there. But I find it unlikely if other homeowners in the neighborhood couldn't hear anything beyond their own doorbell or a shot fired.