Minnesota has a veritable shopping list of regulations. . .new construction, existing dwelling upgrades, rental dwelling, sale or refinancing (and probably another couple that slip my mind at the moment) all trigger slightly to very different requirements for smoke detection. That's for the State. Then local jurisdictions can, and do, ammend as they see fit. Some local fire marshalls have instigated new and/or additional requirements.
As Ron states, the wiring itself, to the smoke detector location, is by the NEC. The location and number of smokes is by other regulation that must be sourced from the AHJ.
