How did DaVinci sleep 15 mins every 2 hours? What kind of alarm clock did he have?

I've been researching the sleep method, but I'm not sure how you can do this without a method to wake you up for the first months or so, did DaVinci have a friend shake him up or something?

How did DaVinci sleep 15 mins every 2 hours? What kind of alarm clock did he have?
big glass of water...
Reply:Sleep researchers have found that sleep patterns are as varied as any other characteristic. Many people sleep very little, and a few don't sleep at all. Internal alarm clocks that wake people up at a desired time are very common. I find the story quite easy to believe.
Reply:I believe he did it himself w/o an alarm clock. I have a friend who has never owned an alarm clock. He doesn't even really mentally prepare himself. He just looks at his watch to see the time then says that he is getting up at 6:30 A.M. or whatever and he is never off by more than about 5 minutes either way. I guess some people just have a greater connection with their subconscious, REM, and sleep patterns than other people do.