the odorless deadly chemical which can be in your house if you have a leaky stove or furnace is CO: Carbon Monoxide.
You have carbon monoxide detectors for that, because it's deadly and can build up without you noticing.
That deadly gas is NOT CO2. CO2 is Carbon Dioxide. You breathe it out, it feeds plants, it's what makes soda drinks fizzy.
So you don't usually have a "CO2 detector" in your home (they exist, though).
Now don't get me wrong: CO2 isn't super healthy either, but since humans emit CO2, we're pretty good at handling low levels of it. Too much of it will asphyxiate you, but that's super rare. It really needs to happen because of things like "nearby volcanic eruptions" and "deep lake water disruptions". Basically CO2 kills you by getting in the way of oxygen that you're trying to breathe in, and it kills you the same way any other gas does: you can't breathe in much oxygen if all the air is something besides oxygen.
CO (Carbon Monoxide), on the other hand, directly fucks up your hemoglobin. You breathe it in, and your blood starts carrying carbon monoxide around, rather than oxygen (in) and carbon dioxide (out). It basically suffocates you at the blood level, rather than the lungs level: You can breathe in all the oxygen you want, but if your blood can't move oxygen, you die.
This also bypasses the "I NEED TO BREATHE!" feeling. You don't notice that your blood is failing to move oxygen, you just get headaches, dizzy, nauseous, and confused, then die.
Carbon Dioxide (CO2): Relatively common, makes drinks fizzy, not dangerous unless there's a a ton of it. If you walk into a room full of CO2, you start choking because you can't breathe.
Carbon Monoxide (CO): Rare poisonous gas, comes from leaky combustion appliances, quite dangerous. If you walk into a room full of CO, you get a headache, act weird, then die.
