Why does the alarm on iPhone keep repeating automatically after 9 minutes?

Why is the default ‘Snooze’ time on iPhone 9 minutes and not 5 minutes or 10 minutes?
If you’re an iPhone user, you’re probably familiar with Apple’s default “haunting” alarm tone and 9-minute alarm snooze time. But have you ever wondered, why 9 minutes and not 5 minutes or 10 minutes?

It turns out that behind it is a long story, to know the story we have to go back many years ago, when the “snooze alarm” button was born, watchmakers were in trouble when they cannot be fine-tuned so that the gears match to delay exactly 10 minutes. And then, watchmakers had 2 options of 9 minutes or 11 minutes, to this day many people are still talking about their choice. However, many people think that 9 minutes is a reasonable amount of time because when going to 10 minutes, people have already entered a deep sleep and make this second awakening make you more sleepy, or simply is that waking up 1-2 minutes earlier is better than “trying to sleep” more. There is also a lot of controversy that Apple’s choice of “Snooze” time of 9 minutes is to honor the first watch model with this “alarm delay” feature. This electric watch model is called 7H241, of Telechron watch company – USA, integrated with an “alarm delay” button with the default time of 9 minutes.