<VV> CO or CO2 ?

[D. Monasterio]

    I start reading on the CO sensors subject several days ago and then it changes to CO2. Didn´t read all messages at all but, it seems to me like talking about the same gas with two names. To me CO is a toxic gas while CO2 is what we exhale in exchange of O2. 
    I think CO2 is not toxic as it is part of the air (a clean... not poluted air) among with Nitrogen, Oxigen and some other gases. 
    Am I right or... need to go back to High School ?

Daniel Monasterio