My alarm went off and the red light starting flashing, I call the fire department, but they did not detect any co. So why did it go off? I did go ahead and replaced it, because it is 7 years old. I also have other levels in my house with a co detector on each level and the other ones did not go off. The one that went off was on the third level in the bathroom and not near a heat source or anything that would cause a false alarm