Facebook Lock (HI App Lock) adds a customizable lock screen to your Facebook that keeps intruders out. It's not the prettiest app in the world, but it's effective and surprisingly not annoying. If you're worried about someone using your phone to get to your Facebook, this is an awesome way to keep them out.
This app is a trimmed-down version of a larger app that locks down more than just Facebook. This particular app lets you set a password to get into your Facebook. During the setup, you'll be asked to set the unlock password. Once you set this, you can proceed to the actual app. Facebook Lock doesn't have many settings, but you can configure how long it will take for the app to relock once unlocked, add it to device admin to prevent it from being uninstalled, set a security question, and set a password. To set your password you first need to choose between the number and the pattern lock. Both are easy to set and function flawlessly. Perhaps it's easier to set a number lock, but a pattern lock could save you from having to peck out a long password every time, which is also very nice. When it comes to looks, the lock screen doesn't match Android's default, but there are some additional themes you can add to make it fit in a little better. Sadly, these have to be downloaded and installed separately. By default, the app's icon is visible in the status bar but you can change this if you uncheck the option in the Settings.
Facebook Lock (HI App Lock) successfully protects your Facebook account from unauthorized access any time you leave your device unattended. The app is free, doesn't include ads, and operates smoothly. However, if you wish to add some additional features such as Hide Facebook Lock, and Fake error message, you need to buy the Pro Key. Additionally, if you want to protect more apps and other sensitive data you might want to download the full app.