Why is the snooze timer on almost all alarm clocks set to 9 minutes? The answer is tradition, and not some highfalutin psychology of sleep.
Users on Quora answered a question very few of us have wondered, but once you hear it, you feel the need to know why.
Alarm clocks have been around since the Ancient Greeks, and Plato purportedly used a water clock to summon his students to lectures. The snooze alarm is a twentieth-century invention, but one which predates digital clocks.
In the 1950s clock makers added a snooze mechanism to the existing gears. By this point the innards of a clock were standardized to the extent that this new mechanism had to fit in with the existing machinery.
One theory is that this limited the options for the length of the snooze to either 9 minutes (and a bit) or 10 minutes (and a bit).
Clock makers opted for 9 minutes and when digital alarm clocks were invented this 9 minute tradition was carried over, despite the fact that designers of a digital alarm clock could have set the snooze to any length. When smartphones replaced bedside alarm clocks, they also set the snooze time to 9 minutes.
Another theory was posted on Quora by David J Slavik. He believes that hybrid-electric clocks with roll-over flip display prompted the use of 9 minutes as a standard time. As Slavik explains:
For this reason the physical interface for the snooze function had to be put on the minute column so that each flip of the card that was displayed when the snooze button was pressed would retrigger the alarm. Putting it anywhere else would have resulted in an inordinately long snooze.
One could argue that even if these theories are false, 9 minutes is the perfect length of time, not too long that deep sleep can take hold but long enough that the snooze feels worth it.
Alarm clocks aren't alone in retaining redundant features that were necessary in previously versions of the product. Cars are still measured in terms of horsepower, despite the fact that horses haven't been used as transport for the majority of British citizens since the mid-twentieth century. The QWERTY keyboard is a remnant of typewriters that has been transposed onto modern computer keyboards. Even humans have the coccyx which is left over from our monkey tail.
So next time you're hitting snooze, feel traditional while you're doing it.