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SCK 2.1 - TVOC and ECO2 (CCS811)

Hey everyone!

This is a quick update for anyone seeing weird values on their Indoor Air Quality (TVOC and ECO2) sensor. The sensor needs a 48h burn-in to stabilize. You can check the datasheet for more information while we work on updating our docs page with all this information. Also after each reset/reboot, it can take up to 20min for the TVOC and ECO2 to stabilize.


We are working to improve our FAQs section with all this information

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A month ago a received my first smartcitizen kit 2.1. After some experimenting I installed it in our kitchen at 2 meters high. The sensor values seemed alright, although the EC02 and TVOC where a little bit high. PM, ECO2 an TVOC reacted as you could expect when we were preparing a meal, toasting a bread or brewing a beer.

Wednesday a received a second sensor which a planned to use outsite. But first I installed it beside the first sensor, just to look at the bandwith of the measures. Most of them are inside the 5-10% difference. That’s acceptable. But the values of the EC02 en TVOC (same sensor) differs very much. The oldest sensor measure at the same moment 1795 ppm and 444 ppb. The newer sensor measures 488 resp. 28 ppb. The kit has run now for 3 day’s, so it couldn’t be the burn-int time. You can find the data at: and

I use a lenovo tablet powersupply whith a quality usb cable on the new kit.

Hi @peterveeling

Thanks for the detailed explanation!

@oscgonfer just released a few weeks ago a section around the ECO2 and TVOC sensor that might help you

RE sensor id:9897
CO2 readings are not real - over 1000 ppm in the woody rural area. The sensor runs for months now.
So the VOC must be suspect too.
Sound dB recordings are not frequent enough - the result is unrealistic averaging.

Anybody similar problems? My sensor is showing way over 2000ppm next to another sensor showing around 600 in a well ventilated space. Cleaning or some calibration necessary?

How long has the sensor been set in that location? Did you have them anywhere else before?

As you might know, the sensor had an initial burn-in time, and after it needs a stabilisation process after each collocation

We tested more than 200 sensors in our lab in the past months, and all of them converged after of maximum of one week

The links above seem to be broken? Can anyone update? Links to that page from the documentation are also broken.

We are seeing some strange readings from our SCK2.1 for ECO2 and TVOC:
At the end of October we have been experiencing regular power outages and the sensor seems to have hit a max reading of ~1830 - is this due to the burn in time? Every time the board resets it should take a week to burn in again?

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Hi! Updated link here: eCO2/TVOC - Smart Citizen Docs


Are the power brownouts coming from your power supply or from the kit?

In principle, the sensor after the burn-in time (initial week) it should take 20minutes more or less for the sensor to give good values again. See: eCO2/TVOC - Smart Citizen Docs

We don’t have easy access to the sensor due to the current lockdown sadly, so I’ve no idea which device is browning out, or if the power supply itself is being interrupted.

Thanks for the updated link.

some weeks ago I got a new SCK2.1 and am very uncertain, why the eCO2 and TVOC readings are so exorbitantly high. I have an older SCK2.1 and put this the days of 28th of March 2023 till 1st of April 2023 right beside each other and the readings are so different. The new one is much after a burn-in time of 48 hours. You can see values of readings here:
New SCK2.1

older SCK2.1

What can I do to get reliable measurements with the new kit?
Thank you

Hello, has nobody a hint, what is with this new eCO2 / TVOC sensor going on? Is it defective?
Thank you in advance