Great question. Carbon dioxide gas is
colorless, odorless, and doesn't react with any
household chemicals, so how can we detect it?
A good way is using a spectrometer. You
use this measuring instrument to shine a special
light through a gas. The gas will absorb certain
parts of that light in a way specific to what
chemical it is: this is called its absorption
spectrum. The rest of the light passes through
the gas and into the spectrometer which
tells you what's left.
To detect carbon dioxide, we usually use infrared
light, so that kind of spectrometer is called an