https://aranet.com/products/aranet4-home

I picked up a pair (indoor+outdoor) of https://www.airgradient.com monitors a few months ago. Happy with them so far though I have not decided on their final positions.

I've been happy with the awair element[1] for years. It also measures PM2 and temp/humidity/voc.

[1]: https://www.getawair.com/products/element

The AZ-0001 Co2 meter. Vendor of a CO2 meter with zero to 2000 ppm co2, 30 or 50 ppm accuracy, serial data output, humidity, and temperature. The meter appears on a big name cheap sales website for a little under $200.

https://www.co2meter.com/collections/handheld/products/az-ha...

One problem with the yellow AZ-0001 CO2 meter is the meter has to be manually restarted if the 9 volt input DC power is interrupted. A second problem is the CO2 value is quite sensitive to my breath when the meter is running on the garage workbench. For outdoor readings the mechanical problem is to put the meter at least 8 feet away from passing humans and also have the meter accessible for restarting.

The same vendor sells a hockey puck device which I have also used. I stopped using the hockey puck due to it's humidity measure device. That was about 4 years ago.

https://lessco2essay.blogspot.com/2015/08/carbon-dioxide-met...

Contact me for a copy of my Python CO2 meter software. The output of the software is lines of unixtime, GPS position, CO2, humidity, and temperature. leemck at gmail dot com.

My CO2 interest is in the global excess CO2 problem.

I really like the airthings view plus which also measures radon.

https://www.airthings.com/en/view-plus

I have a https://www.birdie.design/en-us (I think it was previously called a Canary) mounted in my living room, and it's a great lil device! Overly dramatic, fun, and easy to know whether air quality is good or bad - would recommend!

If you want something that looks attractive in your room and has an app to view history (so the opposite of "hacker"), I highly recommend Awair, been using it for years:

https://www.getawair.com/products/element

You can configure the device display to just show numerical CO2 (that's what I do).

Seeing the CO2 history graphed on your phone might not seem like it's all that necessary, but I find it really is -- you can see how it falls when you're out, you can see how quickly it skyrockets when you turn on the oven, you can see how long it takes to settle into a steady state overnight. Seeing CO2 over time gives me a conceptual understanding of what's actually happening, which I didn't have with my previous CO2 monitor that just showed the current value.

If you want to go DIY route; I use MH-Z19 sensor along with an ESP-32 which has ESP-Home installed on it, works very well and I log the data on Home Assistant.

I have a handful of these in my home and really appreciate the small form factor, long battery life, and options for accessing the data (on-screen live values via eInk display, encoded recent history displayed via QR code, or simple http server endpoint over wifi): https://github.com/davidkreidler/OpenCO2_Sensor. It was straightforward to integrate the accessories into my homebridge instance for ongoing monitoring and notifications as well.

You can make one yourself from the information in the repository or buy one from the author at their Tindie storefront: https://www.tindie.com/products/davidkreidler/open-co2-senso....

The main thing I would consider is that you want a sensor that actually measures CO2, which is usually an NDIR device. A lot of cheaper monitors and even some very fancy professional HVAC devices use “TVOC” meters and calculate a “CO2 equivalent”, and the performance of these devices is wildly variable.

(The AirGradient devices are often configured with CO2 and separate SGP41 TVOC/NOx sensors. It’s entertaining to plot both raw TVOC and CO2 and to observe that they’re clearly showing similar diurnal variation, but the CO2 data is much cleaner.)

Aside: the SGP41 data sheet doesn’t really recommend looking at the raw data, but you can. I have an esphome fork that does this.

If you don't want to go the DIY route, and also are interested in a weather station, Ambient Weather is great. It just works out of the box (the CO2 sensor is an add on), and supports a large pile of local APIs and cloud service integrations.

We went with one of the fancier models, including a nice LCD display and a solid state (ultrasonic) wind monitor, since we get hurricane-level gusts around here. It's held up fine so far. One annoyance: At least the last time I checked, all the sensors have to be in radio range of the base station. It'd be nice if they had WiFi bridges so we could monitor multiple buildings, etc, with one system.

I had fun with this one

https://www.adafruit.com/product/5187

I used a tiny pico and display to make a little clock/sensor

I have been using one of these for years and it is quite nice. https://www.hydrofarm.com/p/autopilot-desktop-co2-monitor-da...

I have an Awair, which is generally good and has a locally accessible API. However, one dick move they did when they shut down (cloud) support for the old Awair, they shut down local API access too. Unfortunately, I was only aware of that after buying the Awair.

I have Apollo Automation MSR-1 (it does multiple things, including CO2 and mmWave movement/presence detection; they also have AIR-1 which tracks all sorts of air quality metrics such as VOC etc), flashed with ESPHome reporting to my Home Assistant setup.

It's main advantage is that it's extremely affordable compared to the competition, and entirely local.

Also I have a Netatmo Indoor Air Quality Monitor (requires their cloud service to work, but there's a Home Assistant integration too) which, alongside PM2.5 and CO2, also does sound and alerts me when music/etc. is too loud.

Some good input on this thread such as that from brendangregg - https://news.ycombinator.com/item?id=34648021

I made two using scd41, esp32 and esphome. https://shop.m5stack.com/products/co2l-unit-with-temperature...

There's a couple things here and it depends on your needs.

The word "track" suggests history.

I've got a https://www.amazon.com/gp/product/B0861777SL which does what it says on the box and works. I've got one in my WFH office and one in my bedroom. There are times when I've woken up from a restless sleep to see that at a higher number (especially in the winter when the house is a bit more closed up). Also the track where I can look at the history and see things "oh yea, last about 4h after I cooked dinner the CO2 went up a bit."

However, that's only the standard sensor stuff (temp, humidity, CO2).

If you've got amazon devices, I've got https://www.amazon.com/gp/product/B08W8KS8D3 ( Amazon Smart Air Quality Monitor ) which sits in my kitchen because I'm interested in other things there too.

I've had some https://milacares.com air purifiers in the house. They work as air monitors and purifiers. I had some issues with them, but they worked for a good while.

Consider if you want instant or historical data. Do you want other data too? What integrations do you have in the house with other home automation? How much DIY are you going to engage in?

I've been looking at the Eve Room, but haven't gotten it yet. It's one of the only devices I found that seems to work with HomeKit.

MH-Z19 module and a WiFi Arduino (esp32) which dumps co2 and temperature into Prometheus.

It's like 20 lines of code and very rewarding to write.

I've used a Sensirion SCD30 (NDIR) sensor attached to a Pi running Grafana, which can be connected to via a web browser.

Airgradient: https://www.airgradient.com

The GQ Electronics GMC-520 has been very reliable for me. It has a Geiger counter and other functionality also.

I have a uHoo for a few years, and it’s still working fine, but the app is pretty bad and the device paywalls the raw data behind a subscription which always felt scammy to me. Also the refresh interval is 1min.

So recently I went the diy route and pretty happy with a setup from m5stack: an SCD41 sensor plugged in to an AtomS3, running EspHome. I set the resolution to 5 seconds (can go down to 1 second), and then data goes to HomeAssistant -> InfluxDB and I plot it in Grafana. Cool to see the quick changes when using gas stove or opening up window.

https://shop.m5stack.com/products/co2l-unit-with-temperature...

https://shop.m5stack.com/products/atoms3-dev-kit-w-0-85-inch...

Honestly? I recommend a VMC. Simply because monitoring allow to let you know something you can already know enough from your feelings, a VMC allow to breathe more oxygenated air.

Genuinely curious, what are the advantages of a CO2 monitor?

I mean, I get you can “track air quality” but what exactly does that mean on day to day basis?

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