How the iPhone Alarm Uses a Clever Design Trick

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When it comes to user interface design, Apple’s work is generally held in very high regard. However, not everything is as perfectly smooth as it appears, or perhaps what you see is just a simplified version of the actual process. A prime example? The alarm time picker on iPhones, which looks like an infinite wheel of scrolling numbers but is, in fact, more complex.

A few weeks ago, a Reddit user shared a screenshot revealing that scrolling through the alarm’s hour and minute options on an iPhone stops at 4:39. To reach this point, you need to scroll for about 10 to 15 seconds on each list. Interestingly, if you scroll upwards, a blank space appears once the timer hits 1:00. Additionally, if your clock is set to the 24-hour format, the picker will stop at 16:39, as first noted by Wccftech.

The curiosity sparked a lot of interest online. When you scroll through the numbers, it appears as though they rotate in a continuous circular motion, but that’s not quite the case. The list of numbers (either 0-12 or 0-24 for hours and 0-60 for minutes) isn’t endless; instead, it’s a finite list that repeats several times to give the illusion of a wheel. Once you’ve scrolled through the repeated sequences, you encounter a limit where scrolling in one direction becomes impossible, and you must reverse to continue.

This behavior isn’t new. Back in 2018, an iPhone user posted about the same 4:39 alarm clock mystery on Apple’s community forums, though the question was never answered. Clearly, Apple’s design choice involves creating a long, repeating list rather than a true circular wheel, which might be intended to simplify the process or optimize performance.

So, what’s really going on? When you reach the top or bottom of the list during scrolling, the timer halts at a specific point, and you have to scroll in the opposite direction to navigate further. This applies regardless of whether your device is set to the 12-hour or 24-hour clock format.

The most straightforward explanation is that Apple implemented the picker as a numbered list that repeats multiple times, rather than a seamless, never-ending loop. Once the list reaches its end, scrolling in one direction is impossible, mimicking a limited range of options rather than a true continuous rotation.