Returning to college teaching mid-pandemic, I bought an SAF Aranet4 Home CO2 meter for measuring my classrooms. It mostly lives in my apartment, waiting to alert me in case I didn't realized I was using my gas range.

There's good evidence predating the pandemic that sufficient air exchange can nearly eliminate respiratory disease transmission. Just as they learned long ago in London that one could eliminate cholera by not drinking sewage water, we understand that the air quality and rate of exchange of indoor air should approximate that of outdoor air. We're however too cheap to do anything about this; it will take more deadly pandemics to drive the needed infrastructure changes.

Do you wince at the idea of people in London drinking sewage water? Those ignorant savages? Yeah, that's how people in the future will look back at us, getting colds and worse all the time in indoor air cesspools.

As we breath out CO2, it makes a great way to measure whether we're changing the air in a room fast enough to keep up with occupant breathing. Wilderness air passed 400ppm as part of global warming. My Manhattan apartment is above the Henry Hudson Parkway, and I can tell the time of day and day of week from the effect of traffic on my CO2 meter. I'm lucky to ever get below 450ppm.

The Aranet works far better than a $30 meter at the measurements a $30 meter will make, such as humidity. By appearance and build quality it's in a different league. CO2 is a bonus.