StandBy (iOS 17 or later) turns a charging iPhone into a bedside or desk display. Requirements: the phone must be charging (MagSafe, wireless, or cable), locked, and placed on its side in landscape. It won't appear while the phone is in use or unplugged.
Any iPhone that can run iOS 17+ supports StandBy. What varies is whether the display stays visible all night: that needs an Always-On display. Those models are the iPhone 14 Pro/Pro Max and later Pro models, plus the iPhone 17, iPhone Air, and the iPhone 18 Pro models. On other iPhones the screen turns off after a while and wakes with a tap.
What it shows: three swipeable views — clocks (many styles, adjustable colour), widgets (your own stacks), and photos. Night Mode adds a red-tinted low-light presentation. Display-on behaviour is controlled in Settings → StandBy → Display (Automatically / After 20 Seconds / Never); with MagSafe, the phone can even remember a different view per charging spot.
Always-on does use some power, but the feature is designed around idle low-power rendering; the practical effect on battery health over a night is small.
Sources: https://support.apple.com/guide/iphone/iph878d77632/ios · https://www.apple.com/iphone/compare/
— Osnivo Guides