Why should you have a CO2 monitor? Because CO2 is a good proxy for aerosols that humans exhale, and aerosols are what carry airborne diseases like COVID-19. So if you’re stuck in a box full of people, checking CO2 is a good way to tell if you should mask up or get out before you get infected. Those being the options generally under your personal control. If you’re in an environment over which you have some kind of influence, like your residence or a health-conscious business, you can use readings over 800 ppm (parts per million) as a signal to open the doors or windows or turn on the ventilation.
Gross analogy to make the point: Would you drink a beer full of some rando’s backwash? No. Well, CO2 is also a great indicator for how much of the air in your lungs came right out of someone else. Like a big communal liplock, no kidding. Neglecting masks, as most of the US does, what comes out of them goes right into you.
| CO2 ppm | Rebreathed Fraction |
| 420 | 0.0% |
| 600 | 0.5% |
| 800 | 1.0% |
| 1200 | 2.1% |
| 2000 | 4.2% |
| 2800 | 6.3% |
| 3600 | 8.4% |
| 4400 | 10.5% |
The Vitalight caught my attention because it was described as “an acceptable alternative” to the Aranet4 by the inimitable Naomi Wu, aka @RealSexyCyborg on Twitter. The Aranet4 is a rock-solid CO2 monitor that I highly recommend (and resell, so there’s your conflict of interest statement). But you’re going to pay for that quality, my friend. And if $250 is a bit much stacked against the rents you owe your phone company, ISP, streaming services, insurance companies, and every other money leech hanging off you, then a Vitalight might be a reasonable tradeoff between cost and quality.
Because everything is a tradeoff! The big tradeoff the designers of the Vitalight made was a nice bright screen that sucks electricity out of its rechargeable battery like an IT salaryman sucking down caffeine and adderall to make the code drop . Burn bright, baby, burn bright. That screen allows frequent updates, but only lasts about a day and a half, in contrast to the Aranet4’s e-ink screen that only updates once a minute, but runs for months off a couple AA batteries. And on the Vitalight you’ve got to hit the on button to see the reading, as it goes to sleep every 60 seconds to try and preserve battery life.
The other real suck with the Vitalight is that it (well, my test sample of 1 unit) typically reads about 100ppm lower than an Aranet4 (NDIR technology). I also compared it to a monitor based on a Sensirion SCD-41 (photoacoustic tech) and saw the same discrepancy. This was after following calibration steps. Part of the problem is that the Vitalight is programmed to think that it’s 400ppm out there in the big wide world. Which is currently true on top of Mauna Loa, but… not so much in cities where most of us live. My little 292K city runs about 450ppm in the hood. So the Vitalight is starting 50ppm low out of the gate. Anyway, 50-100ppm low is something to consider given 800ppm is when the CDC says you should start ventilating.
Pros:
- Cheap – $44 on Amazon
- Small & light – 78 gm with handy clip
- Bright, colorful display
- Color-blind friendly (tricorder style triangle points at risk index)
- Audible alarm at 1000ppm, easily silenced
- Auto sleep to preserve batteries
- USB-C charging
Cons:
- Runs ~100ppm low compared to an Aranet4 (and SCD-41)
- Gotta keep mashing that “on” button (even if it’s plugged in)
- Poor battery life (compared to e-ink)
- No history
- No Bluetooth, no app
- Only USB-A to USB-C charging, not C-to-C
- You’re going to be able to replace the battery when it dies.
Suggestions for The Designer:
- $ Set your calibration point to something more typical for a user’s outdoor environment.
- $ Leave it on if it’s got external power. Probably just a code tweak, considering you already built in a LiPo charger. Just check power on start, and don’t start the sleep timer so long as it is there.
- $ Give us some history! A bar chart for the last couple days would be cool.
- $$ Add a resistor to make it work with USB-C to C
- $$ Put an inductive coil in the back shell so we can keep it topped up with a charging pad.
- $$ Add an accelerometer so it wakes up on movement or a tap.
- $$$ Use a better sensor. The SCD-41 is a great choice.