There are already unpickable locks on the market.
My MIL also had an unpickable lock. Both lived in NYC, in apartments with concrete walls, and solid doors. My MIL’s probably could have been drilled out faster than her brother’s was, though.
Try to keep the posts on the same field please.
As an aside, most exterior doors on homes used to swing outwards. Strap hinges were mounted on the outside of the doors so they could be secured with nails that were clinched on the inside, meaning bent over, double clinched in the case of doors so the nails were bent twice on the backside so the ends could be pounded back into the door and the nails couldn’t be pulled out from outside. Concealed door hinges that we use now were developed in conjunction with the manufacture of screws that could be used to secure them in a door frame.
The the phrase ‘dead as a doornail’ may simply be alliteration in a figurative description, but possibly arose from the idea of a wrought iron nail that had been twice bent over was ‘dead’ and could no longer be pounded out straight for re-use.