Hi Damjan,
Now, instead of the bird, the most non-ecological method of determining CO and CO2 concentration, what about?
1) Putting a lambda sensor (that one used in cars). If the O2 concentration falls and you know the gas produced (CO2), you can determine its concentration. The electronic could be an AD converter and a 805X controller.
2) Another way to measure CO and CO2 concentrations is the infrared method. cO and CO2 gases absorb a part of spectre of infrared (I think it's wavelenght is near 1000 nanometer). This sensor is used on car carburator and injection adjusting systems.
Save the canaries.....
Regards to all
:-)