It depends on how the carbon monoxide was produced and why it reached you, and often more than one party shares responsibility. The property owner or landlord may be responsible for maintaining the appliance and providing a required detector. A heating or plumbing contractor who installed or serviced the equipment improperly may be responsible for that work.
And if the appliance or detector itself was defective — poorly designed, lacking adequate safety features or warnings, or simply failing — the manufacturer may be responsible under product-liability principles. In many cases, the failure involves a combination: a poorly maintained appliance and a missing detector, for example.
Sorting this out depends on tracing exactly how the exposure happened, which is a job for experts examining the appliance, the venting, and the maintenance and detector records. Because that equipment can be repaired or replaced quickly after an incident, preserving it is one of the most important early steps — and it is what identifies every responsible party.