Cool, thanks for the clarification. Indeed it's a good and practical idea for a small app. As other comments have said, (some) people might happily pay for this app.

I luckily won't need such feedback loop anymore, had some mild lower back pain show up over 10 years ago and bought a chair without a backrest that, after 3-4 weeks of struggling, trained me to sit up straight. Now I have some random cheap office chair with a backrest, but I rarely lean back to it. Funnily, I was going to give up using that "backrestless" chair after 2 weeks of inconvenience, but decided to give it one more week and then the magic happened :-) Mild lower back pain automatically gone.

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hn8726 4 hours ago | parent [-]

Care to share an example of this backrestless chair? Is it like a regular chair just without the backrest, or has some other differences? Does it have armrests for example, and if not - does it bother you?

	▲	tanelpoder 4 hours ago \| parent \| next [-]
		I went with an overkill approach at first (as I often do :-) and bought some expensive nicely designed "active chair" / stool that was adjustable high enough so that I could lean on it even when using my desk as a standing desk. It was interesting, but not a game changer at all for me. I don't use standing desks now at all. But what I have now is this: https://www.amazon.com/dp/B002FL3LY4 Just don't assemble the backrest at first. If sitting up straight, I just lean wrists on my keyboard wristpad and part of forearms on the desk, no armrests needed either. Edit: I still use my height-adjustable standing desk, but now it's value is that I could adjust it for the perfect height for my sitting-up-straight position (so no chair armrests needed) and it's been fixed at that height for the last 7 years...
	▲	manuelmoreale 4 hours ago \| parent \| prev [-]
		Not sure which one the parent was referring to but personalizing I've been using one of these for more than a decade at this point (I'm sitting on it right now) https://www.varierfurniture.com/en/products The one I have does have a backrest but because of the way it's shaped you don't actually use it to slouch. It's more there to support when you lean back and want to take a break from typing or something like that.