In addition to the national standard, there can be state and local standards as well. Your local fire department should be able to tell you the requirements. New construction will likely require hardwired. Massachusetts also has regulations for photoelectric and ionization sensors. Regulations are having a difficult time keeping up with the new technology, so many states are still catching up with things like wireless interconnect and mobile notification. There are a couple hardwired smart smoke/CO detectors in the works (Birdi and Halo), but they’re still working on certification. There’s also the Nest Protect, which has a hardwired option, but it only has wireless interconnect so it may not meet your regulations. Until then, to meet new construction requirements it’s probably best to use traditional alarms. To integrate with SmartThings, you can then wire in a relay or use a listening device like a Leeo or Kiddie RemoteLync. There’s lots of info in this community for all those options. Here’s a link to adding a relay (which I hope to do myself, some day).
The ZCOMBO works well for retrofit of older construction that doesn’t require hardwire or traditional interconnect, although it would be nice if they interconnected.