iOS 18.1 added a new ‘Inactivity Reboot’ security feature for iPhone

Last week, a report from 404 Media highlighted concerns from law enforcement officials about iPhones rebooting automatically rebooting themselves.

While law enforcement officials had erroneously speculated that iPhones were secretly communicating with each other to reboot, that’s not actually the case. Instead, Apple added a new security feature in iOS 18.1 that forces iPhones to reboot after a period of inactivity.

The change was first pointed out by security researcher Jiska Classen on Mastodon. According to Classen, this “Inactivity Reboot” feature is designed to automatically reboot an iPhone if it hasn’t been unlocked within a certain period of time.

According to a follow up report from 404 Media, citing comments from Corellium founder Chris Wade, the reboot occurs after four days. This means that every time an iPhone goes more than four days without being used, it will automatically reboot itself.

The change has been a point of frustration among cops who say it makes iPhones stored for forensic explanation harder to unlock. After a reboot, an iPhone will enter the Before First Unlock (BFU) state and become significantly harder to unlock. It’s generally easiest for an iPhone to be unlocked or “cracked” in the “After First Unlock” state.

But while reporting so far has largely focused on the impact this change will have on law enforcement, it will also put another protection in place against thieves and other bad actors.

Matthew Green, a cryptographer and associate professor at Johns Hopkins University, noted in a statement to 404 Media:

“Remember that the real threat here is not police. It’s the kind of people who will steal your iPhone for malign purposes. This feature means that if your phone gets stolen, the thieves can’t nurse it along for months until they develop the tech to crack it. I would bet that rebooting after a reasonable inactivity period probably doesn’t inconvenience anyone, but does make your phone a lot more secure. So it seems like a pretty good idea.”

Apple hasn’t commented on this change, but you can view the relevant code changes in iOS 18.1 on GitHub.