What's the nonsense part? My CO detector is meaningful at about 11 or so. It also doesn't give peak readings; if I smoke up the basement, the CO reading goes up (15, or 20-something if it's really smoky) and then drops as I air it out. I told him not to worry about it, OTOH long-term exposure to low levels of CO, while not dangerous, can still cause malaise and flu-like symptoms.
BTW, the one time my detector went off and there actually was a dangerous level of CO, there was no smoky smell at all. CO was over 100 and rising rapidly.
Regards, Bob