Google Galaxy Nexus Android mobile technology platform 4.0 Users Guide - Manual (Page 102)

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You can choose among these lock options, listed in approximate order of strength:
G Slide provides no protection, but lets you get to the Home screen quickly, or open Camera and start
taking pictures immediately.
G Face Unlock lets you unlock your phone by looking at it. This is the least secure lock option.
G Pattern lets you draw a simple pattern with your finger to unlock the phone. This is slightly more
secure than Face Unlock.
G PIN requires four or more numbers. Longer PINs tend to be more secure.
G Password requires four or more letters or numbers. This is the most secure option, as long as you
create a strong password.
Important For best security, specify a password that is
G A least 8 characters long.
G Contains a mixture of numbers, letters, and special symbols
G Doesn't contain any recognizable words or phrases.
Related settings
Settings > Device > Display > Sleep
Settings > Personal > Security > Make pattern visible
Related topics
Use the lock screen
Encrypt your phone