Aranet4

Quality CO₂ sensors are pricey. I previously had two from AliExpress, but both were unreliable and eventually broke. I finally got an Aranet4, and it’s been flawless for over a year so far.

I use Aranet devices myself - https://www.aranet.com/en/home/products/aranet4-home What you could take from them is how prominent the current measurement is on the screen. I can glance over from a distance and instantly see the number. The colours get inverted if it goes into the red zone, so I can glance at it from across the room without my glasses and still see whether it's bad or not. From what the simulator shows, with your device I'd need to lean in pretty close to understand what's going on. And blinking light indicators are tricky - you can easily catch it between blinks and look away content that everything's alright.

aranet4 CO2 monitor that I bring with me. 2xAA batteries allow it to go for a year or more, and I can pull the readings via Bluetooth to my phone to look at historical data. As sneak also replied, it's just a proxy: higher CO2 correlates to higher chance of breathing in pathogens, but doesn't take into consideration filtration.

I have several CO2 monitors including some from AirThings, Aranet4, and a industrial sensor in the form of a Vaisala GMP252 CO2 probe. They all track closely enough that I don't worry about it. The Vaisala is rated to +/- 40PPM which is accurate enough for living space environmentals.

> there’s not much you can do with a residential AQI sensor without adding a bunch of other automation controls. You don't need automation. I have a portable CO2 monitor (aranet4) and it gives me an indication of how effectively the air is being exchanged. I've learned that my desk location at home is ok during summer and winter, but when temperatures are moderate the furnace isn't running as much, and the CO2 will get quite high. I keep a window cracked when I work there and it's enough to bring it down to reasonable levels. I didnt know this information before getting it. Similar when I was visiting relatives over easter - the CO2 in the bedroom got up to 2500ppm wile I slept (old house, sealed tight but no forced air circulation). I opened the window for the rest of my stay.

Devices like the Aranet4 are mainly useful for telling you how well ventilated a space is relative to how many people are breathing into it, which is a very good proxy for viral load and viral risk. It's pretty much only in spaces with high quality air filtration (aka high CADR for cleaning an enclosed environment) or significant far-UVC protective measures that the proxy relationship breaks down, and the breakdown will always be an overestimation of risk from the CO2 monitor, never an underestimation. For those reasons it's a very useful tool to have to put an upper bound on the risk of the space you're in and help you make informed decisions about whether you can e.g. hold your breath and take a drink under far-UVC cover or not. PM2.5 sensors or other things like what you're thinking of do have their place, but they also have a bunch of other issues - they'll be detecting VOCs, brake and tire dust that's fine enough, any aerosol whether it's coming out of a mammal or not. I think it's inaccurate to say they're just a generically better solution than CO2 monitors for viral risk.