For Android: learn the hard reset combo for your phone, especially if you encrypt it.
After rebooting, pattern/PIN will be required to decrypt the phone. Biometrics won't work for this step. This is what graphene does for security, tries to keep the phone in a "before first unlock" state by rebooting on a timer. You can't even read anything over USB/ADB, it's scrambled until you unlock the phone.
The only drawback to just keeping your phone in this state is none of your apps are loaded, so no notifications/updates/processing at all.