I have two of them, one inside and one outside. They both go down to roughly 400 ppm and the indoor one goes very high when it's all cooped up inside. The outdo

I have two of them, one inside and one outside. They both go down to roughly 400 ppm and the indoor one goes very high when it's all cooped up inside. The outdoor one fluctuates since I'm in an urban area. I believe they are accurate to within about 10%. During the smoke event, they combined with my indoor/outdoor pm2.5 sensors have been extremely useful.