ok guys, I came down to my garage for several minutes to read the manual/label. Basically, it says the alarm won't go off with only 70 ppm or below, can't change the setting. Also, the one I got from HD has the AC adapter, with battery back up in case power is out. The test is to test the alarm, not only the battery. The warranty is around 7 years, but before it expired, it will blink, then it's time to buy a new one.
I'll test the exhaust later today when I am off work.
Vash, nice if we are close, but I am not sure if I need this thing or not. I just get it for extra security. Recently, I smell something around the house once in a while, and don't kno what it is. Link for detail below.
http://forums.pelicanparts.com/off-topic-discussions/673702-please-tell-me-what-smell.html