What are you all putting in your garages? I am concerned that smoke from welding might trigger a conventional smoke alarm. My shop will be 28x50 with a 12 foot ceiling.
I've never thought about a smoke detector in a garage... if I'm not in it, I won't hear an alarm either, so seems it'd need to be a remotely monitored variety.
I'm a low voltage contractor and install commerical fire alarms and home security systems. I always had rather install heat detectors in garages because of the problem with dirt, dust and smoke from cars, mowers and gas powered yard tools. They trigger by temperature at 135 degrees, instead of smoke.
Without a home security system to tie into, I'm not aware of a stand alone heat detector.
I like the ideas of the heat and co2 sensors. I'd never really thought about anything in the garage, but I'll bet more fires start in garages than just about anyplace else in the home.
Although bad cooks could account for a lot of kitchen fires!