CO2 Sensors

Violet reviews the Vitalight and Aranet4 CO2 sensors:

The rates went up fast. But instead of lagging, the Vitalight overtook the Aranet immediately, the number racing up in real time. When the Aranet refreshed, it was catching up to the Vitalight but still behind it. The Vitalight was telling me this was bad now, while I was waiting on the Aranet to give me the reading.

The Vitalight's alarm went off at 800 (beeping twice) as its arrow moved from green to yellow. The Vitalight number raced higher and the Aranet refreshed again -- now closer to the Vitalight. The Vitalight's two-beep alarm went off again as its risk category arrow moved to Orange. I was ready to flee but waited for the Aranet to refresh -- and then it did, at a higher number than the Vitalight, having overtaken it.

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6 Responses:

  1. jwz says:

    Can't wait to aim my SodaStream at one of these bad boys.

    • Zygo says:

      I exhaled a full breath on mine, and it screamed for minutes.  A SodaStream sounds like cruelty to robots.  Cruelty that I'd eagerly watch on YouTube, mind you.

      The English manual is an interesting work of translation because the product is clearly designed around requirements for covid--it references standards from 2020 for preventing "high risk of mass infection" and the form factor, low precision, and alarm feature are useless for any other purpose you'd need to monitor CO2 for--but it never mentions covid by name anywhere.  It's for "air pollution" instead, like someone did a global search-and-replace after a lawyer noped anything that could lead to an FDA enforcement action.

  2. Wout says:

    Cool, I was just yesterday looking at affordable but accurate CO2 meters and didn't find any, and now it turns out there's a bunch in this price range.

    The important this is to look for an NDIR sensor. The very cheap meters normally use a meter that detects volatile organic compounds and then use a lookup table to decide how much CO2 that is.

  3. Juggle says:

    I've had my eye on the aranet for while but couldn't quite justify the price.  Last week I saw some talk on Twitter about the vitalight and decided for $40 it was worth a try.   (It appears to also be available here under a different name:  

    It claims to be an NDIR sensor so reads actual CO2 not just inferring it from VOC like most of the cheap sensors.  And I confirmed that putting it into a bag with a bit of alcohol it didn't max out.  It did go up about 75-125 but didn't max out like the VOC sensors do.  

    Mine behaves a little differently than Violets did though - I don't get an alarm at 800, just at 1200 (which what the docs that came with mine said as well) and then a constant alarm above ~2400.   

    Battery lame.  The first day or two it seemed ok.  But Saturday it didn't even go 12 hours on a full charge.  Probably mostly because of how often my daughter was checking it...but still, that really reduces it's utility.  If you only check it hourly or so - it might get the 2 days the mfg claims.  But today I've only checked it maybe 5 times and the battery is already 50% down after 6 hours.

    I also haven't been able to get mine to go through a calibration following the steps in the instructions - but it does drop to 400 when I go outside, and in my car with the AC on recirculation mode it will fairly rapidly get up to 1200 (i.e. within about 5-10 minutes)  switching the AC out of recirculation mode the numbers drop back down to 400 almost as quickly.   I'm don't really trust the actual readings too much - but I do trust it as at least a relative indicator of CO2 concentration.  

    I was kind of surprised to find just how bad the air in my home is.  Without me there (just my dog) it never gets much lower than 560, with me it gets around 700...and overnight in my bedroom I'll hit 1200 even with a ceiling fan going for circulation.  Has me wanting to get more houseplants and look into upgrading my HVAC as well as wondering if this may explain why I so seldom feel rested after a "good" nights sleep.

    My office, which is a small freestanding building about 1,000sqft with 4 or 5 of us working there I was pleased to see stayed at 400 for over an hour with me by myself...and with 3 co-workers here it still stays around 650.  Guess that's one benefit to an old building with a lot of air leaks.  

    This weekend I had to go to PHX to get my daughter who was flying back from visiting my parents - I opted not to bring it to the airport just because I didn't want one more device to deal with going through security (she's a "young traveler" so I had to get a special pass to meet her at the gate.)  I was pleased to find she was quickly obsessed with it.   She reluctantly masked at school last year - but she isn't very good about wearing it properly.  Having the CO2 meter to show her how risky places are has really got her thinking about risk.   

    At our hotel she was excited to show me that in the big lobby with just us an a receptionist it was reading the same 400 it did outside.  And the elevator, hallways and our room all were 500 or less which we both found reassuring.  Heck, the hotel room had lower CO2 levels with the 2 of us than my own home with just me.

    We also stopped at the AZ Science Center and were again pleased to see numbers no higher than 600 anytime we thought to check it.  Though given the close proximity of other people we both still masked.  So props to the Science Center for some impressive air handling.  

    We stopped to pickup pizza and she ran in to get it...then ran right back out saying "Oh my god, it jumped right to 2000 as soon as I stepped in there and I realized I forgot my mask!"   (And even though I'm glad so chose to mask voluntarily I still explained to her that the pizza ovens are likely to make the CO2 in there higher than "normal" because I want to her think about what the number really means and why it may be higher or lower in certain places.  I'm not just trying to scare her into being better with her mask.)

    She's excited to bring it to school next week when she starts back up - she's trying to make bets with me on how high the numbers will be in her various classes.  

    For $40 it's been well worth it, I'd still like an aranet or some other known reliable sensor to compare it to for some validation...but I really can't complain for the price and have found it pretty interesting seeing how far off my gut was about ventilation in some places.

  4. Nate says:

    There have been a variety of these cheap NDIR-based sensors recently. I've tested them against the Aranet4 and they seem roughly accurate. There was one that needed to be recalibrated before it read reasonable levels but it worked fine after that.

    Here's one that's $30 currently, and there are many copies of this same reference design. Just make sure you test a given model+source with a known good sensor before committing to buying many (e.g. for school etc.)

    I like the Aranet4, especially after they fixed the X/Y axis scaling in a recent update of the iOS app. You can get it for $200 or a bit less, and it's good to support an independent creator who puts effort into polishing their product.

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