So tell me about these CO2 sensors and what you’re really measuring with them. What they’re measuring is the concentration of the gas carbon dioxide, which we exhale in our breath…. When we exhale, the air that comes out of our lungs has roughly 100 times the concentration of carbon dioxide as the outdoor air. If we’re in a small poorly ventilated room, our sitting around, even if we’re not very active, really increases that carbon dioxide level quite a bit. You’re basically measuring, you can see whether the air that I’m breathing in has already been breathed out by somebody else.