Best smoke, fire amd Carbon Monoxide detector for ST?

There’s only one on the official “works with SmartThings” list, a zwave device from First Alert. It’s a very basic device, in particular, it doesn’t trigger the other smoke detectors that you have and it doesn’t announce which room the alert is in. ( that’s what “doesn’t work with onelink“ means.) If I recall correctly, you also cannot turn off the smoke detector from the app. You Have to physically press the button on it

Some community members use the nest protects which have many more advanced features and there is a community created integration for those.