Recently, a report from 404 Media raised alarms from law enforcement regarding incidents of iPhones unexpectedly rebooting themselves.
Although officials initially speculated that iPhones were covertly communicating to trigger these reboots, this isn’t the case. Apple has implemented a new security feature in iOS 18.1 that prompts iPhones to restart following a period of inactivity.
This change was first noted by security researcher Jiska Classen on Mastodon. Classen explained that the “Inactivity Reboot” feature is intended to automatically reboot an iPhone if it remains unlocked for a designated time frame.
Following up on this, 404 Media cited Corellium’s founder Chris Wade, who mentioned that the reboot takes place after four days of inactivity. This means that if an iPhone is unused for more than four days, it will self-restart.
This modification has caused frustration among law enforcement officials, who argue that it complicates the process of unlocking iPhones stored for forensic analysis. Once rebooted, an iPhone enters the Before First Unlock (BFU) state, making it significantly more challenging to unlock. It’s generally simpler to access an iPhone in the After First Unlock state.
While much of the focus in reporting has centered on how this change affects law enforcement, it also enhances security against thieves and other malicious individuals.
Matthew Green, a cryptographer and associate professor at Johns Hopkins University, emphasized in a statement to 404 Media:
“It’s important to remember that the primary threat comes not from law enforcement but from those who may steal your iPhone for harmful reasons. This feature means that if your phone is taken, thieves can’t keep it operational for long periods while figuring out how to crack it. I would wager that a reboot after a suitable inactivity duration shouldn’t inconvenience anyone, yet it greatly enhances your phone’s security. It seems like a smart move.”
Apple has not yet addressed this modification, but interested parties can view the relevant code alterations in iOS 18.1 on GitHub.
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