Infosec News

GrapheneOS provides an auto-reboot feature which reboots locked devices after a set period of time to put data at rest. A countdown timer is started each time the device is locked, and the device will reboot if a successful unlock doesn't occur before the timer reaches zero.

https://grapheneos.org/features#auto-reboot

Essentially it drops the decryption key derived from your unlock pattern / code. Attacks to access files while the decryption key is loaded, even if the phone is locked, are mitigated. The only things that works after a reboot are phone calls, SMS, and the alarm clock. I have mine set to reboot every 4 hours of inactivity.

I believe this feature is to not only to mitigate your average attacker but also law enforcement threat levels who purchase exploit kits. Can't do much without the decryption key so they are left with slow brute force attacks.