You can't and won't because the truth of the matter is that police very frequently wait outside during anything even remotely resembling a hostage crisis, and a

You can't and won't because the truth of the matter is that police very frequently wait outside during anything even remotely resembling a hostage crisis, and a gunman holding a gun to your face inside your house isn't even ambiguously a hostage situation. The street cops who respond to this won't have any interest in running into the building to get shot, and they'll use concern for you as their excuse not to do it. They'll wait outside and call a hostage negotiator if you're lucky, or just yell at the building with loudspeakers until the gunman gets bored and gives up or shoots you in your face. If you're very lucky, an hour or two later a SWAT team might show up, but there is a good chance they'll stall for time too.