Apple quietly introduced code into iOS 18.1 which reboots the device if it has not been unlocked for a period of time, reverting it to a state which improves the security of iPhones overall and is making it harder for police to break into the devices, according to multiple iPhone security experts.
On Thursday, 404 Media reported that law enforcement officials were freaking out that iPhones which had been stored for examination were mysteriously rebooting themselves. At the time the cause was unclear, with the officials only able to speculate why they were being locked out of the devices. Now a day later, the potential reason why is coming into view.
“Apple indeed added a feature called ‘inactivity reboot’ in iOS 18.1.,” Dr.-Ing. Jiska Classen, a research group leader at the Hasso Plattner Institute, tweeted after 404 Media published on Thursday along with screenshots that they presented as the relevant pieces of code.
It’s not that simple. iOS has a really sophisticated system for deciding which things to keep in memory and which to evict, and it only does that when it needs more resources. Choosing which apps to kill is based on how recently an app was used, how much of share resources are in use, how often the app gets used, if it’s doing background processing, and other more subtle signals.
Usually if people notice apps being killed when in the background a lot it’s because one of the apps they’re switching to is using a lot of resources, which forces the eviction of other apps.