For your safety and well being. It is recommended that you install and properly maintain at least these 4 detectors. While many don’t install a oxygen depletion detector. It is highly recommended as a safety device for use in confined spaces. An open flame/radiant heat source may not generate enough Carbon Monoxide to kill you in marginal conditions. But such a device in a small under ventilated space, perhaps like a teardrop or small cargo. May consume enough oxygen to pose just as much of a hazard as Carbon Monoxide does.