That was my exact first thought. That seems to be a lot more complicated than a traditional bell, except for the fact that you don't have to run two wires there

That was my exact first thought. That seems to be a lot more complicated than a traditional bell, except for the fact that you don't have to run two wires there (a thing most places will already have there). I mean this could be a okay solution for a very certain set of circumstances, but making your visitors scan a QR-Code seems like bad UX, why not have them fill out a form while you're at it? If I had a situation where it was impossible to run wires through the wall I'd install a old-school knocker on the door and a knock sensor on the inside. UX is intuitive and the knock sensor can still send me things to the phone if I like that.