Not for long! [1] It's an unconfirmed rumor for now; but perhaps we're heading there.

> The iPhone 15 Pro and Pro Max will use a new ultra-low energy microprocessor allowing certain features like the new capacitive solid-state buttons to remain functional even when the handset is powered off

[1]: https://www.macrumors.com/2023/03/20/iphone-15-volume-mute-b...