I assume we are talking Carbon Monoxide (CO) detectors. I think there are codes regarding placement of CO detectors in the NFPA. If you have any questions, you could also contact an alarm company that is Lffe/Safety licensed. For the most part, there needs to be one for each "sleeping compartment". Think about NG or LP detectors if that applies also.
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I do the things that I must, and really regret, are unfortunately necessary.

RIP OBG