Is there an easy way to tell a watch device from a non-watch device in code?

Is the reported screen sizes the only way to tell, or is there another simple method to tell if the device running a widget is a watch or not? Knowing that widgets can behave differently on watch devices vs non-watch devices, I would like to add some additional functionality to the non-watch devices. Is this possible, or should I look at splitting the app into one for watches and a different app for non-watches?