For many of us, there is the time we're supposed to wake up and the time we actually wake up. The device which makes all this extra sleep time possible is called a snooze button. This button essentially resets an alarm clock for a limited amount of time, allowing the user just enough time to fall back asleep before reality strikes again. While a snooze button can be activated for several cycles, eventually the alarm clock wins. Some modern alarm clocks also have "sleep" and "nap" buttons as well.
There are a number of theories about the 9 minute cycle of a snooze button. Some believe that it takes approximately ten minutes for the average person to reach what is called Stage 1 sleep, essentially a quick dozing off. In fact, the first alarm clock with a snooze button, introduced in the 1950s by General Electric, offered either a five minute or ten minute snoozing option. It was only when the LED alarm clocks became popular in the late 1960s that a 9 minute cycle became commonplace.
Another theory about the snooze button cycle is that engineers looked at earlier alarm clock models and decided that 9 minutes was a good enough standard to follow. Studies conducted on volunteers supposedly indicated that most sleepers wanted anywhere from five to ten extra minutes of sleep, so anything under ten minutes should be acceptable. It's not unusual for heavy sleepers to hit the button several times anyway, so they would be actually be getting nearly a half-hour of additional sleep.
There are those who suggest the snooze button is actually worse for the sleeper than waking up with the alarm or using no alarm at all. The additional sleep time provided is not enough to allow the sleeper to reach the satisfying Stage 5 or REM sleep cycle. Instead, a sleeper almost reaches the lightest Stage 1 cycle before the alarm sounds again. If this cycle is repeated several times, the sleeper may actually be adding to his or her level of sleep debt. Some sleep experts suggest using the snooze button very sparingly, if at all. It might be better to set the alarm to a later time and spend the extra time taking an invigorating shower instead.