Please rebut my points as I am happy to be proven wrong.
I would, if they would even refer to what I’ve said.

1) I am an analog guy.
I can’t disprove that.
2) As I posted, the arduino solution requires almost no effort. (I have not done the exercise myself to check for gotchas, but I will).
Except writing
and testing software. I stress the second part.
3) Arduinos are cheap. Depending on where you are...under $8. Yes, a 555 and a couple of caps and resistors are cheaper--I grant you that.
By mentioning Arduino I meant it in comparison not only to the analog solution, but to digital alternatives. They’re much more expensive than even the corresponding microcontrollers themselves — not to mention anything needed for that task. Even with in the software domain this can be done at under 15% of Arduino’s cost.
4) Arduinos are reliable. Can you site a reference that supports this reliability concern?
I have never said Arduinos are not reliable. I claim that the software solution is
less reliable. That arises from orders of magnitude higher complexity of both the underlying technology and the design, harder testing, less previous testing and higher chance of making a mistake in the first place.
(1)5) I have used Arduinos to make a reliable "bucket-level-detector" for my tractor. Works fine in a relatively harsh environment.
I was never talking about the environment. And if you did, I am happy you made something working. But your success doesn’t prove in any way that there are no better solutions or that someone else may repeat that with similar outcome.
6) Yes, it is fun to solder up a 555 dip package on a perf board and hang some resistors and caps around it with wires here and there to connect to the PIR and buzzer. My lab is full of that stuff. Well...maybe put it on a pcb, no? OK, I do that too...fab my own pcbs when I want to stain my hands with ferric chloride, or slap one together and send it to expresspcb (that aint cheap).
We do not know what the author has. We are on the electronics forum, so — unless clearly stated otherwise — it is a sane assumption that if someone wants to build an electronic solution, they will have to build a circuit on a PCB. Isn’t it?

Consider it a kind of a joke (I don’t suggest doing that), but with the 555 circuit presented above, you can go without a PCB: dead bug potted in epoxy or lowe temperature hot glue.

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(1) The easiness of turning an idea into software and its seemingly shallow learning curve misleads many people into false feel of comfort, despite their software is far from being reliable.