What car maker is not providing keys? As far as I know, app control is optional.

I read somewhere, the suggestion, that the filter be replaced when air flow has reduced by 50% from when the filter is new. IDK, that seems reasonable to me and should be measurable.

I have always replaced filters on a schedule, but it has always felt wasteful. Sometimes the filter is clearly dirty and sometimes it is not. I would like something more specific.

I will look into PMS7003.