While 400 is the usual average for outside, below is not impossible. If you have lots of plants and few people, co2 might drop.
If you really want to know if it works you need real calibration. If the results need to be really accurate, I would not go for self built devices anyway but hire or buy (semi)professional gear, which is calibrated and does not rely on autocalibration.
The T6615 has it’s own gas supply for accurate self calibration, unlike all of the other sensors I am aware of which need periodic exposure to outside air to deliver accurate readings. I’m still surprised it doesn’t get more coverage, especially since esphome support is very good for it.
Maintaining a calibrated CO2 meter is crucial for accurate readings, whether commercial or DIY. Users should understand their meter’s operation and calibration steps. DIY projects often provide deeper insights than off-the-shelf devices.
Regarding outdoor plant influence on CO2 levels, while significant alterations are improbable, basic knowledge is essential. I advise calibrating meters in fresh, unconfined air.
Additionally, from my experience, many commercial CO2 meters suffer design flaws, providing a false sense of quality. For more insights, please refer to my blog post:
Are CO2 Meters Homemade as Reliable as Commercial CO2 Meters?
While the T6615 is indeed a dual-channel CO2 sensor, there are several other dual-channel CO2 sensors available, such as the widely used Sensirion SCD30. This sensor, priced at a fraction of the T6615’s cost, operates at 3.3V (unlike the T6615, which requires 5V), consumes less power, and offers higher precision.
An important point to note is that dual-channel sensors also need periodic calibration to maintain accuracy.
I appreciate the mention of esphome support for the T6615. However, it’s important for users to explore multiple options before making a decision. The Sensirion SCD30, for example, provides excellent performance at a more affordable price point.
For more information on the Sensirion SCD30, you can visit the following link: Sensirion SCD30 Dual-Channel CO2 Sensor
I bought one SCD30 with ESP32 for test purpose, but I’m not able to get it working. I followed instructions in article on emariete. When the web tool uploading configuration to ESP, shortly after “Wrapping up” I’m getting an error:
Serial port is not ready. Close any other application using it and try again.
I tried restart computer, use diferent computers, cables, but still same.
The second issue is that I’m affraid that I have some problem with connection because I also tried install basic configuration from Sensiron via Arduino IDE, but in serial monitor I’m still getting error:
Error trying to execute blockingReadMeasurementData(): Received NACK on transmit of address
Could someone please help me to solve these issues?
For those who might be interested, I just finished the MoreSense MS-06 based on the Sensirion SCD40. It can easily be connected to HA via MQTT or REST (yaml). I have been working with the SCD40 for quite some time now and it turns out to be quite reliable. I did several comparison tests with the Aranet4 which is considered quite accurate and the results are very comparable. One can turn off the auto calibration (ASC) and also calibrate with a reference value.
Airthings Wave works well here. Smooth direct integration via Raspberry Pi built in Bluetooth. Connection drops occasionally, but not too badly. What is a bit disappointing is that HA doesn’t seem to retrieve stored data on Wave, so the app shows no gaps in history, while HA shows gaps. But overall I am pleased.
Currently working on a CO2 Sensor for ESPHome (part of the “Made for ESPHome” program). I posted a topic over here and would love additional feedback!
Did anyone tested the SwitchBot Meter Pro (CO2 Monitor)?
If so, can you:
Hey,
yes i have it connected to HA. The Meter Pro CO2 is connected via the Switchbot Bluetooth Integration. So directly via Bluetooth without any hub.
The firmeware update can be done via the switchbot app also without the hub but i see no way todo this via HA directly.
At the moment, I think that Senseair S88 is the best.
Hi, i see this one popped up on my aliexpress page
Has anyone tried it?
DAIKIN Air Sensor BRY88AB151K/BRY88AA151K Geek to meets ESPHome Home Assistant. Sensor content temperature, humidity, CO2, PM2.5
https://a.aliexpress.com/_oo8WRB3
It seems references to AirGradient ONE are missing 
I use an outdoor version but the also offer indoor versions with all the usual measurements: temp, rh, CO2, VOC (index, not ppm) and particulate matter (PM2.5, PM10, PM0.3).
They are not cheap however (135$ for the kit) they have a very good track record of accuracy and publish very openly about advancements and also problems that arise. And it is open source hardware and directly available in HA as a local polling device 
The indoor version is bulky however, probably only useful if you put it on a wall or something. We used several AirGradient indoor at a site I was working and it was very insightful for knowing what processes are most polluting, when too many people are in the room and the ventilation cannot keep up etc.
The Switchbot CO2 Sensor seems to work reasonably well if you connect it to HA via Bluetooth. Strangely, I had to remove the batteries from my unit for it to work properly when connected to USB-C…
Been using the One for about a week now, can highly recommend it. I went with the fully assembled kit and the only time you need to access the web interface is for the firmware updates, everything else is local and handled via the HA integration page for it.
It’s been a boon in having a visual of the Co2 levels in my unit so I know when to open a window and to have the fan mode on the AC turned on to promote airflow more and reduce it to more safe levels.
I use this with the graph card for at a glace visuals on the side monitor and on my phone when I have it open:
type: custom:mini-graph-card
entities:
- sensor.airgradientone_carbon_dioxide
align_icon: left
align_state: center
show:
fill: true
labels: false
color_thresholds:
- value: 600
color: "#1AB24D"
- value: 1000
color: "#9BC73E"
- value: 1500
color: "#FBC711"
- value: 2000
color: "#F29126"
- value: 2100
color: "#EE1D23"
hours_to_show: 6
points_per_hour: 5
theme: Metro Blue
icon: mdi:molecule-co2
The colors and values are based on this chart:
What Entities does it expose.
I bought one to test and play around.
First I updated the FW via Smartphone and the SwitchBot App.
Then I saw that Home Assistant already found something … the SwitchBot Bluetooth integration found a “Light Strip DD90”. But the only entity it had was sensor.light_strip_dd90_bluetooth_signal
A few minutes later it added light.light_strip_dd90.
Of course, nothing can be controlled or read out with it, as the sensor is not a lamp, but a CO2 sensor with temperature and humidity sensor
yeah had the same. do you have active scans on?
or
Still looking for feedback on this, as we are planning the first production run
The Switchbot Meter Pro CO2 works perfectly now via the Bluetooth Integration.
It has since replaced my Netatmo Setup.
I am quite happy with the performance. At first it seemed a bit bugged, but with the initial Update it got a lot better and when you remove the batteries and leave it running on USB C it was been absolutely rock solid and very responsive.
We have the Aranet 4 and after reading this and other topics I added this device to HA. Now I also get temp and humidity readings as a bonus.
The Aranet 4 is expensive. We paid around 160 euros for it and prices have gone up. We needed a solid and accurate meter during COVID. But now that we have it I thought I’d just give it a try!
