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Alarm clock and 9 minutes of sleep

by admin

Waking up one morning I was seriously puzzled by the question: "Why do all the alarm clocks I’ve had over the past few years delay (snooze) ringing again for exactly 9 minutes ? Why not 5 or 10? Or for example by 12 ?" This question interested me so much that I decided to google the topic a bit and thoroughly poke around in what I found.
Versions of the constant’s origin
As a result of searches I found quite a lot of different versions. I have divided them into a couple of sections, which are presented below.

Funny versions

  • Five minutes is not enough. Ten minutes is plenty. Nine is not much different from ten, and it looks appropriate. The number of seconds in nine minutes is pretty close to 2^9=512. The next degree of two is too far away.
  • The frequency of the electric grid in America is 60Hz. Nine minutes is 60*6*9=32400 cycles, which is pretty close to 2^15=32768.
  • The reason is still in the mechanical alarms, in which for some mechanical reason this was chosen.

Plausible versions

  • Psychologists have found that "going back to sleep" for more than 9 minutes brings a person back to a deep sleep.
  • The study group confirmed that they were more comfortable completing 8-12 minutes of sleep (But why not 10 or 12 ?).
  • The first snooze clocks manufactured in the late 50’s had a timeout of 9 minutes. That’s how it’s been going ever since.
  • The nine-minute interval can be tracked by observing the value of one (last) digit.

UPD: It became clear from the comments comments that there are other options. I wrote about my alarm clocks – SE cell phones (k550, and some other), iPhone

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