This feature allows you to set up a code that you must enter in order to use the device after its screen has been turned off.
Different types of screen lock are available, with varying degrees of convenience and security.
Some of these options, such as Face unlock or Pattern, may also ask you to set up a back-up PIN or password in case the other method fails or is forgotten. It is important that this back-up code is made secure (not easy to guess), otherwise it becomes easy to bypass your unlock screen.
Screen lock types
None / Swipe
Disables the screen lock. You will usually still see your device's normal "swipe to unlock" screen. Some devices may offer both None and Swipe options, in which case None truly removes all lock screens including the "swipe to unlock" screen.
Unlocking the screen requires you to trace a secret path between a pattern of dots on the screen. You will be asked to make up any path between the dots consisting of at least four line segments, and will need to repeat this pattern each time you wake up the device. This provides a relatively high security, because it is hard to guess. The path your finger traces on the screen, however, may leave a noticeable streak on the front glass of your device, which can be used to figure out your pattern.
PIN requires you to record a number consisting of 4 or more digits, and re-enter this PIN each time you wake up the device. This provides a relatively high level of security.
Requires you to record a password string consisting of 4 or more characters from a keyboard. You will need to re-enter this password each time you wake up the device. This provides the highest level of security out of these options.
Unlock options not available on all devices
Motion unlock offers an alternative to the usual "swipe to unlock" screen. To unlock, you just need to touch the screen while tilting the device sharply backwards or forwards. This provides no additional security as it requires no secret to be remembered.
Unlocking with Face unlock takes a picture of your face with the device's front-facing camera, and uses facial recognition technology. If it matches your face, the device is unlocked. This feature provides a low security level because the facial recognition is relatively easy to fool: holding up a photo of you will usually unlock the device.
Face and voice
Offered on some devices, Face and voice is a variant of the face unlock that can also record a short voice command and later use voice recognition technology along with the facial recognition technology. This feature provides a low security level due to the low accuracy of the facial and voice recognition technologies.