I agree with Xronger, don't buy stuff you don't need....

It is pretty common here to see people who installed CO
detectors in the all electric houses! Why? stupid TV shows
that scare people into thinking they need CO detectors.

Don't take my word for it... Buy detector, run furnace
set your detector 2 feet away and look at the reading.

If it reads "0" return detector back and save your money
for the furnace inspection every one - two years.