Smokes and CO detectors are required to have a distinctly different alarm sound. I have no idea if the residential combo devices alarm through other devices (read smokes), but I would think that they don't. I have not yet tied the two together, but I may be wrong.
Interesting, I have worked with ADA/ADABAG ( a US standard for accessibility containing the Law for government and non-government installations) and though I provide notification for the deaf for smoke, I have not for CO. I will have to research this.
