iPhone restarts itself: When Apple's security function causes problems
After 72 hours of inactivity, iOS 18 automatically triggers a reboot. This may cut the mobile connection. What you can do now.
(Image: Sebastian Trepesch)
A new security function in iOS 18 provides more protection, but causes problems in certain use cases. If an iPhone is not unlocked for a period of 72 hours, it automatically restarts itself, as security researchers have analyzed. The automatic restart also cuts the mobile connection if a SIM PIN is set. This is likely to be the case frequently in Germany if an older, physical SIM card is still being used in the iPhone.
iPhone can no longer be reached
As a result, the iPhone can no longer be reached by phone and the location can only be tracked temporarily and to a limited extent via Apple's "Where is?" network. This can cause problems in both private and professional use: If a field worker leaves the iPhone on the charging station in the office on Friday afternoon and takes it to the next appointment on Monday afternoon without unlocking it first, it has already restarted. The phone is therefore not available for calls as usual.
If an iPhone is used purely as an emergency phone with location tracking, for example for senior citizens or younger children in the family, it is not only calls that fail: The cut mobile connection also restricts location tracking. Although the iPhone goes into an AirTag-like mode after restarting, it can then only be roughly located for around 24 hours via "Where is?", as security researcher Jiska Classen explained in a follow-up to her detailed analysis of the function.
Location determination can also be less accurate during this period, especially if the iPhone is located in less densely populated areas. Common Where-is functions such as playing a sound also do not work in this mode.
Workaround: Disable SIM PIN
Apple has neither confirmed nor denied the function, which was apparently introduced with iOS 18.0. Originally, this was apparently designed for a period of 7 days of inactivity; iOS 18.1 shortens this to 3 days. Users cannot switch off the automatic reboot.
However, users can prevent the mobile connection from being disconnected: If no SIM PIN is activated, the iPhone logs back into the mobile network and remains accessible – even after a restart. The option can be found in "Settings > Mobile network > SIM PIN" or "Settings > Mobile network > [SIM name] > SIM PIN". The SIM card is of course no longer protected by its own PIN, so a thief could read it and continue to use it until it is blocked by the mobile phone provider.
In normal everyday use, users should practically never run into an inactivity restart, as the iPhone is regularly unlocked and the timer reset. And if it is left without an additional power supply, the battery will usually run out before the 72 hours are up anyway.
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