The distinct sound requirement is in the IBC 909.9.2. I have yet to find references requiring CO alarms, I am sure I am just looking in the wrong locations (we do have one jurisdiction in Utah that has a law requiring them in all residences).
I will have to get back to this in a week, those who know the IBC and ADA are all gone today and I am out all next week. I am interested to know myself.
