+1 about corner'd cat's web page. I recently read the article about the polite/societal rules and I couldn't agree more.
Our latest house is not the most secure (a lot of windows/doors) but the previous owner did put in motion-sensitive outdoor lights all around and a solid wood front door. I wouldn't know how to install those myself (yet). So my contribution has been battery powered devices from Walmart. I found these cheap (but useful) door/window alarms that go off when the magnetic portion of it is separated from the main body. I put them on our most vulnerable windows, and set some to ring a friendly but loud chime on all of our doors that lead to the outside. Also from Walmart (or was it lowe's?) I found some sliding locks that were easy to install. It took a tiny bit of getting used to but now my wife and I are accustomed to sliding the bolts closed/open every morning. Those went on the front door and the bedroom (also our fall back room). If it came to a chain vs. a decent sliding bolt, I'd choose a bolt. The sliding bolt is closed at the same time the doorknob is engaged which would combine their strengths or at least overlap a bit better. That is unless the knob is turned (but ours is kept locked) - and even then that would mean whoever is battering the door would have to keep one hand on the doorknob which would limit momentum. With a chain a potential habit would be to open the door for everyone and only have the chain as protection. Or if the door were being pushed/battered, the doorknob would fail and then the chain would have to work alone. A sliding bolt directly into the floor is typically stronger than one that engages a metal loop screwed into the door frame. I wasn't able to do that with my sliding bolt (metal plate was in the way) but it's easy to engage/disengage with a foot before going out. But yes, these just buy time. Maybe that rubber door stop isn't a bad idea even if you do other things as it would engage if the door were still to open and buy you even more time. (these ideas of course or just in theory, who knows how it will pan out in real life)
This is just an opinion, but I still feel it's better to speak through the door for the first part of a greeting if anything is in question. It's only as rude your voice is - no more so than speaking through an intercom at an apartment complex. Doors aren't soundproof - they can probably hear you just fine. Any family/friend probably wouldn't mind, and they already have your phone number and wouldn't have a problem identifying themselves. If it's a friend you next fling the door open wide and it's all smiles. But if it's a stranger the closed door gives you time - to think, be mentally prepared and make a decision. Even if it's just to say "sorry I think I'll pass on the Super Concentrated Enzymatic Cleaner today (for $80 cash), but thanks and good luck!"
The habit of flinging the door open first thing (some still choose to because of odds or they're armed) - puts you behind the curve as you'll have to identify who it is/isn't and what's going on, and then decide what to do. And if they can see you they know exactly who/where/how many you are and what you've got.
Think of it like being able to screen phone calls with caller ID - same principle and enjoyed by many. But with a more serious second function too.
I was going to suggest roleplaying but that might feel a bit too condescending. A milder version would be to ask her to help you with an experiment - something like:you're curious to see how well people can hear from outside the front door. Start a back-and-forth conversation about something as you go outside and while still talking shut the door and continue the conversation with her. She'll at least have had an exposure.
It sounds like you have a Beretta handgun already.
If that's true you can purchase snaps caps and get her started practicing safe gun handling, function, loading/unloading, and dry firing (and safety again). Even malfunction drills. She can pretty much learn everything short of experiencing the recoil/blast, looking at the groups to verify good sight picture, and re-acquiring the target. You may have already started on this. But even if the range were available to her, it helps a new shooter to learn everything first without the confusion of the explosions going off all around and trying to hear instruction through ear muffs+plugs. Then later just add ammo (at the range of course). To an extent you can even check her trigger control by watching for front sight movement towards the end of the break. One drill I've heard/tried is to balance a quarter/penny/dime on the front sight and dry fire without it falling. (except the front post on my revolver is massive so it's not very hard)
It can be a fun time together. Even though I had been shooting quite a while I went to a short NRA pistol course (just a few hours long) with my wife and we had a good time. (well, I did for sure
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That's just about everything I can think of.