Can pattern unlock be used for my device’s lock screen after I enable full device encryption?
I normally use pattern unlock, but the encryption procedure requires me to change to PIN or password before proceeding. Can I revert to pattern unlock once the encryption procedure is complete?
Important Note: The following answer is based on Android 4.0 (Ice Cream Sandwich). Beginning with Android 5.0 (KitKat) it is possible to encrypt one’s device using a pattern. However I have not tested if it is now possible to use a different security mechanism for boot unlock and screen unlock.
No, after encryption you must use PIN or password for your lock screen.
I could find no official documentation on this, so I tried it experimentally. I took a Nexus S running Android 4.0.3 (Ice Cream Sandwich), set a PIN lock, and performed the encryption procedure. After this, all unlock options other than PIN and Password are disabled (greyed out and inaccessible).
I suspect that the reason for this is that in order for the device encryption to be reasonably secure, it must be protected with a PIN or password to be entered at boot time, and Android settings do not provide a way to specify two different unlock methods for boot-time unlock and lock screen unlock. Maybe Android will gain this feature in a later version.
Note that there is no way to unencrypt your Android device without performing a factory reset, which will erase all of your data.
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