I don't live in an area where the sun can wake me up regularly, and I have a spouse to boot, but I do wake up without alarms. It took a bit of doing, but after shifting my schedule so as to be a morning person about 18 years ago, after a couple years of waking up to an alarm, I found I was waking up 1-2 minutes before my alarm. So one day I stopped setting it, and for the last 15+ years I've found my body naturally wakes me up at the same 5:30am (+/- 5 minutes) every day.