So like: air sensor ($) -> air purifier ($) -> filters for previous ($$$ over time) https://en.wikipedia.org/wiki/Razor_and_blades_model https://en.wikipedia.o

So like: air sensor ($) -> air purifier ($) -> filters for previous ($$$ over time) https://en.wikipedia.org/wiki/Razor_and_blades_model https://en.wikipedia.org/wiki/Razor_and_blades_model