[1FreeAmerican]

Most alarm companies also install CO and smoke detectors, and if in fact they died of CO poisoning this could have been prevented.

My neighbor's HVAC went sideways while she was at work and the alarm notified her and she called the FD. When they showed up the CO levels were over 400ppm - loss of consciousness in less than a minute and death in 3-4 minutes more. Fortunately her dogs were in the garage.

[1FreeAmerican]

I am also about to install some safety devices - network connected CO and Natural Gas monitors (in addition to the standard smoke and CO detectors already installed) and a solenoid operated valve on the main gas line.

Cost in the $500 range.