You can use a screen lock to prevent unauthorized access to your phone. Types of screen locks include:

• Face (Android 4.0 and later)
  
  Face lock uses the front facing camera to match the face of the person unlocking the phone to the face of the person who set the lock. Face lock requires you to set a backup lock method (pattern or PIN) in case the camera cannot achieve a match due to issues such as poor lighting.
  
  
• Pattern
  
  Pattern lock uses a pattern which you draw on a 3x3 grid to unlock the screen. Pattern lock can be bypassed after five failed attempts by entering the credentials for the phone’s primary Google account.
  
  
• Pin 
  
  Pin lock uses a PIN (Personal Identification Number) you have defined, to unlock the screen. PINs are 4-16 digits long using characters 0-9.  PIN lock can be bypassed after five failed attempts by entering the credentials for the phone’s primary Google account.
  
  
• Password
  
  Password lock uses a password you defined, to unlock the screen. Passwords are 4-16 characters, alphanumeric and case sensitive. Password lock can be bypassed after five failed attempts by entering the credentials for the phone’s primary Google account.