yes, they are unreliable. I have seen brand new out of the box alarms put in a ziploc bad and filled with 100 ppm CO from a can and the alarms NEVER went off. Not after 1 hour, not after2 hours, not after 3 hours. How much CO is safe in your home 0 ppm. The UL lab wont put their approval on them unless they have been dumbed down so they dont go off with low levels of CO. Low levels at sustained periods of exposure can be very harmful.
Where can I get a quality CO DETECTOR? Is this even a reasonable request? What do you have in your home?