An unofficial test of a Very first Alert Design CO606 Carbon Monoxide Detector. After I made this video, I found another video which confirmed my findings. http://www.youtube.com/watch?v=2M28lRzyEcI
There they state Fire Fighters placed on masks at 35 ppm CO! (Whereas the First Alert will not alarm until 400 ppm.) In the abovementioned video, they show an unit which responds very quickly, Precisely what I was trying to find.
The NSI 3000 looks to be a good deal. The most significant bang for your buck. See http://www.youtube.com/watch?v=vgMBMN8BuQk