A newly discovered security feature in iOS 18.1 is forcing iPhones to automatically reboot after periods of inactivity, making it significantly more difficult for both thieves and law enforcement to access locked devices.
The feature, dubbed "inactivity reboot," automatically restarts Apple iPhones that remain locked for approximately four days, as revealed in an investigation by 404 Media. When an iPhone reboots, it enters a highly secure "Before First Unlock" (BFU) state, requiring the original passcode for access.
Law enforcement officials first noticed the issue when iPhones stored for forensic examination were mysteriously rebooting themselves. Christopher Vance, a forensic specialist at Magnet Forensics, has already advised police officers to prioritise collecting evidence from iOS 18 devices while they're in an "After First Unlock" (AFU) state, before the automatic reboot occurs.
Dr.-Ing. Jiska Classen, a research group leader at the Hasso Plattner Institute, confirmed that this isn't a bug but an intentional security feature implemented by Apple in iOS 18.1. The feature's existence was verified through code analysis, as reported by 404 Media.
Matthew Green, a cryptographer and associate professor at Johns Hopkins University, explained that while the feature affects law enforcement, its primary target is criminals. "Remember that the real threat here is not police. It's the kind of people who will steal your iPhone for malign purposes," Green told 404 Media. He added that the feature prevents thieves from keeping stolen phones active for months while developing techniques to crack them.
Chris Wade, founder of mobile analysis company Corellium, detailed that the timer activates when an iPhone is in a locked state, automatically triggering a reboot after the four-day period. This forces investigators or potential thieves to start their attempts to access the device from scratch.
The feature represents Apple's latest effort to enhance iPhone security, though it has created new challenges for law enforcement agencies conducting forensic investigations on seized devices.