I have the Aranet4. Pretty expensive (220 eur) but I'm very happy with it. During the reconstruction of our house, we are sharing a bedroom with the kids. It's

I have the Aranet4. Pretty expensive (220 eur) but I'm very happy with it. During the reconstruction of our house, we are sharing a bedroom with the kids. It's cold, we close things... First night I saw CO2 go up to 2500 ppm and I got up to open windows. I had headaches every morning, that's gone now (I do have cold nostrils now though). And now I'm using it to check all spaces, I'm going to need some active ventilation in almost all rooms it seems like. I feel that CO2 ppm is a good proxy for measuring the need for ventilation (which is also needed when cooking, moisture etc). I'm using the hell out of the device. It's nice that it will probably last >1 year on a standard battery. One device in every room would be cool, coupled to Home Assistant to steer Blauberg ventilation units or something... The Aranet is too expensive for that, so great to see developments like this.