Inactivity reboot" effectively puts iPhones in a more secure state by locking the user's encryption keys in the iPhone's secure enclave chip.

With iOS 18, Apple introduced a feature that causes the iPhone to reboot every three days, security researchers have confirmed (via TechCrunch). In

Apple's iOS 18.1 auto-reboot feature locks iPhones after four days, blocking easy access, but at the same time, frustrating law enforcement in forensic probes.

However, the explanation is actually much simpler. Referring to the feature as an "inactivity reboot," AppleInsider says that this reboot timer isn't based on network connectivity or the phone's charge. Rather, the reboot simply occurs after a specific length of time -- around 96 hours.

A new iPhone security feature in iOS 18 will make it tough for forensic analysts to obtain data from a locked device

Apple covertly inserted a new security feature in iOS 18.1 that automatically prompts iPhones to reboot after 72 hours of inactivity. Read more here.