I usually use proto.io to mockup and then test prototypes right from the device. However, proto has yet to include this functionality for smart watches. (I can only test in browser). Does anyone here have any ideas on how to test right from the device (without creating the actual app)?
Paper prototyping is a quick and dirty way to do early usability testing. You can do that on a watch UI in the same way you do it for desktop/mobile UIs. Just print out your prototype screens and perform a usability test, swapping out the printouts as if they were live screens.
Here's an example (skip to 3:00).