This might be a good Roomba mod project…“Grower is a small ‘rover’ vehicle which navigates around the periphery of a room. It hugs the room’s walls and responds to the carbon dioxide levels in the air by actually drawing varying heights of ‘grass’ on the walls in green ink. The Grower robot senses the carbon dioxide (CO2) level in the air via a small digital CO2 sensor.” Thanks James! Link.