I've been using the Awair Element for years. It helped me decide to install an air exchanger an to swap the gas range with induction. Bonus, it has a local API for pulling data.

I have a purple air sensor outside. One day I'll get around to making the air exchanger smart enough to turn off when the smoke from fires makes the air outside worse than inside, it turn off the air exchanger when inside air is good enough, etc.