Apple Watch wake up alarm

I have a wake up alarm set in the sleep app on my iPhone & watch. My watch goes into sleep mode at the set time & shows that a alarm is set. When it's time for the alarm to wake me up it goes off from my iPhone not my watch. How do you set it up so the watch wakes you up & not the iPhone. Also how to change from iPhone to watch or vise versa. Finally how do you set the watch to wake you up using the vibrate function?

Thanks