Even in the early hours of the morning, when you're repeatedly hitting the snooze button to catch just a few more minutes of sleep, you've probably wondered why that beloved feature only gives you another nine minutes in dreamland. Nine minutes seems like an arbitrary timeframe. Why not make it an even 10? There's a good explanation for it—and it's all in the original alarm clock's design.
By the time the snooze feature was added in the 1950s, the innards of alarm clocks had long been standardized. This meant that the teeth on the snooze gear had to mesh with the existing gear configuration, leaving engineers with a single choice: They could set the snooze for either a little more than nine minutes, or a little more than 10 minutes. But because early reports indicated that 10 minutes was too long, allowing people to fall back into a "deep" sleep, clock makers decided on the nine-minute gear, believing people would wake up easier and happier after a shorter snooze.
Although today's digital clocks can be programmed to have a snooze of any length, many default to the standard nine minutes, because that's what consumers expect.