This made me question my own alarm. I tested it, and it seems to function
correctly.
however, I'm not sure where it should be placed. Reading online some say
that the detectors should be placed on the ceiling, because the CO is mixed
in with the warm furnace air that rises. However, the person who checked
out my co workers house said that the CO generally falls, and so the
detectors should be lower to the ground.

There should be instruction in the package telling you where to put
the thing. If you don't beleive them, get two, and put one high and
the other low. It's not like they're expensive.