Can you be more specific? Are you talking just on mobile?
For watches and such on mobile, the device maker has to write software that runs on the watch, but interacts with the mobile OS’s API in order to display information. It connects to your phone as a subscription device to things like alarms, messages, notifications and calendars. So if whatever app you’re using on your phone routes events through these systems, they will work with your software.
If you’re talking about integrations with desktop software, I’m unaware of any watch devices or device OS’s interact with anything like that.