ADT CO2 sensors reliable? Where to place?

[canyonblue@xxxxxxxxx]

I have heard mixed messages from several alarm companies about CO2
sensors. Some swear by them, others have stated a high level of falses
with mointered CO2 sensors. I am inclined to get mointored CO2 sensors
through ADT but I don't want falses... do they false and if not, where
should I place them? I have heard some say near the source of CO2 like
furnances, the kitchen, the gas dryer, the gas fireplace ... but then
again I have heard to just place one near or in the bedrooms. Thoughts
on placement and number I should have?