idkbutfreakingout on "CO2 monitor effectiveness?"

So after a couple of months of finding nothing (but 3 people being bitten all the time), I bought a BEAP CO2 monitor and have put it in a room where we have received bites, but where nobody is sleeping tonight.
I am hoping to either get confirmation or to move on and figure out what the next thing could be if not BB.
Has anyone used these and how effective are they for a one time use?