All joking aside, using a straw is a good way to do rough testing of CO2 detectors. You put a couple of cups of water in a container, use a piece of airline tubing as a straw and huff and puff thru it to build up CO2 in that water. I was able to get to 10 ppm without major effort. By repeating the huff and puff about every 15 minutes you can keep that level too. But, never do this while standing! Hyperventilating while standing isn't good!