I know for a fact that my Levoit unit isn't that sophisticated because when it asks you to replace the filter there's simply a button which resets the filter li

I know for a fact that my Levoit unit isn't that sophisticated because when it asks you to replace the filter there's simply a button which resets the filter life back to 100% that you're supposed to press after changing it - if it were actually doing anything clever to determine the state of the filter then you wouldn't have to tell it that it's been replaced, it would be able to tell on its own. I suspect it's nothing more than a timer which triggers the warning after running for some hardcoded number of hours.