Building a cottage in northern Michigan and notice that State Code requires smoke alarms be wired for AC, in each bedroom, hall and main living area but they also require that they are all interconnected so if one goes off they all alert. Battery backup is required on each as well.

Does the interconnection use a two conductor wire between each unit, and what size wire is used? I can provide the AC to each but need to know the type of wire to interconnect. Any advice?