Call it paranoia.
https://www.google.com/search?q=defective+carbon+monoxide+detector&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a

Having lost several relations to carbon monoxide, I feel this is rational.

I have two carbon monoxide detectors, purchased five years apart.

They are from different manufacturers.

They are tested twice per year.

I replace one unit every ten years.

http://www.trulia.com/blog/KathleenTurner/2010/12/help_it_s_1am_and_my_carbon_monoxide_detector_is_going_off

defective carbon monoxide detector
https://www.google.com/search?q=defective+carbon+monoxide+detector&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a

.