Getting carbon monoxide poisoning symptoms but alarms don't go off?

As a owner of a fire alarm and gas detection company (www.trifectafire.com),I have found it is a common misconception that combination detectors can be used for detection purposes being placed on the ceiling surface. Carbon monoxide is heavier than standard air therefor carbon monoxide specific detectors should be placed closer to the floor level as opposed to smoke detectors on the ceiling when smoke rises. I hope this helps in your issue. Also commercial gas detection devices are available, not only for carbon monoxide detection but for other gases to include oxygen depletion. Please also consider you may have mold that causes all the same symptoms within the walls. For questions specific in this area please consult a environmental consulting firm who can take air samples and determine the cause.