My company installed a burglar alarm @ a residence in Hingham and the local fire marshal would not sign off because there were line voltage smokes (installed to code) and wireless smokes that reported thru the burglar alarm system (not installed to code) in the building.
He said that we would have to choose one or the other and if they were going to be the wireless smokes we would have to add more because they were installed as supplementary to the line voltage smokes. I believe his reasoning was that when both types of smokes go into alarm that the sounds will be different and not synced causing the HO to become confused. We removed the wireless smokes instead of adding so many more.
I remember in a code class that I was taking a while ago the teacher was teaching this same thing. That you could not install to separate systems because of the difference in the smoke's alarm tone.