(Disclaimer: I keep an alarm clock as backup. But most days I can wake up before it rings.)
Sleep is one of my obsessions. For most of my life, I had trouble waking up on time for school or work. A few years ago I discovered that I could wake up on time without an alarm clock (or more accurately, wake up before it rings).
How to get up without an alarm clock:
Is it not elementary, my dear Watson? Do this for a week or two and soon you will find yourself awake before the alarm clock rings.
Both you and I know very well that there are devils hidden in this simple method. One of them is the bedtime. A consistent bedtime is required for this to work ;-)