I don't use an alarm, except for timing food in ovens. I wake naturally, every day, around 5, 6 if I'm lucky (see time of posting, lucky weekend).
Fitbit reckons I get an average of 6 hours sleep a night but I don't believe it. I'm asleep within 10 minutes of being in bed at somewhere between 9 & 10 and wake between 5 & 6. I'm not awake for 2 hours of that, I'd remember. It's bollox.
I'm awake enough when I wake to get on a rowing machine or a bike in less than half an hour and am never late for work which starts at 08:00 whether at home or on site.
In the summer I wake earlier but I go to bed earlier. I think I'd like more sleep (who wouldn't) but this has been my daily routine for at least 10 years so I reckon it's probably OK.