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

A new feature introduced on iOS 18.1 could make it difficult for law enforcement officials to gain access to seized devices for forensic analysis.

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