Fun fact: humans do not have oxygen levels detection, but do have CO2 levels detection. Your body would ring all kinds of the alarm bells if CO2 levels rise above the norm, even if there is enough oxygen.
Either way I was referring to other chemicals that plants remove from the air, not CO2.
Examples: https://www.google.com/search?hl=en-CA&authuser=0&biw=1345&b...
Depending on choice of pot and soil, most only need to be watered once a week. Even still, there are decorations that hold water to slow release for even extended times between watering. Great for vacations, or the forgetful.