How did people wake up before alarm clocks were invented?

The question of waking up pops up every so often on the subreddit, so we have a few previous answers to draw on. As always, more posts are always welcome!

u/frogbrooks examines one way they did it in Islamic cultures;
u/Bodark43 looks at how a blacksmith's apprentice might do so;
and u/rocketsocks considers the experience of time.