This stuff is no joking matter. I've known too many people either killed or really messed up with CM poisoning. When we built our new house all was great till fall when we used the heat - we kept getting headaches, wife even went to the doctor and discovered CM poisoning from a blood test. Bought a CM monitor and first night goes off in the middle of the night. So the search was on for the source- it's a brand new freaking house man! So here's what happened - 2" PVC pipes, 1 in 1 out for the burner of the furnace- The morons glued up the intake and just press-fit the exhaust pipe. It was a 50/50 guess on their part but got it wrong. It was pumping CM into the basement. After that, she's put every monitor known to man all over the place *such drama those gals* which paid off again one winter when we had so much snow (feet and more feet) that blocked that same exhaust pipe.