Before bed, I consciously think about the time I want to wake, and then will usually do so just before the desired time. Once in a while I'll wake a few minute

Before bed, I consciously think about the time I want to wake, and then will usually do so just before the desired time. Once in a while I'll wake a few minutes later. As someone who's been able to do this for almost 30 years at this point, I'm convinced that I actually peek at the clock in some semi-conscious state. I have no recollection of doing so. I wouldn't be surprised to find that other external factors are part of it. The brain is amazing at noticing with it thinks is important and filtering out other things (I once lived across the street from an elevated subway stop and didn't notice a weekend shutdown until Sunday evening). We may not be consciously aware of the signals that the brain is using to wake up. That said, I've retained the ability regardless of season, location, etc. I can do it just as well on day one of a business trip in another timezone, which is one of the reasons I think I'm somehow noticing the clock. If I had to make a completely wild guess, I'd say that I'm somehow noticing the clock and some stress hormone response to that causes me to come out of sleep more frequently as the desired time to wake approaches. I'm not sure what's healthier, but when I wake myself up vs. the alarm (on the days my wife sets an alarm earlier than I plan to get up), I'm generally ready to get up and go when it's NOT the alarm. With the alarm, I'm groggy, tired, and cold.