Rule of thumb in any liability issue: Dead people dont sue.
And yes Mark, they suck. They are NOT what the average person thinks they are. They are NOT a sure fire way to measure anything...and, does anyone know that after 5 years you are supposed to toss them? Who, honestly, has replaced a unit that is more than 5 years old? Who really knows how long its been there unless you just put it up? ITs why some of us install units that not only know, they make sure YOU know. The public wants cheap, so First Alert and others give you cheap. Just dont bet your life on it. Something is better than nothing, but personally, I would not have one of those POS things in my home. And the new combo smoke/CO detectors? Jokes.