Out of curiosity, why are these out of sync? Putting a sync protocol on the output circuit that the sounders are connected to will synchronize them if sync is desired
Sounders aren't connected to an output circuit. They're either controlled by the addressable initiating device loop or, in some cases, by the detector itself for local alarm purposes. It is possible to put a reverse polarity module on the IDC to synchronize and, in some cases, change the coding of the sounders (usually to temporal 4 for CO alarms). Either this system doesn't have said module installed, or the sounders could be set to output only for local alarms, which wouldn't necessarily require audible syncronization.
