A free program for Android, by RJ Developers.

Are you looking for an additional layer of mobile device security? Or are you just tired of people borrowing your phone and opening your messaging or personal apps without permission? Well, whether you are looking for one or the other, the Smart AppLock app will surely be of help to you. It is a dependable utility program that lets you lock up your apps behind a PIN or pattern. With it, you can rest assured that your personal applications are kept private and only you can access them.

Furthermore, you can customize the lock’s settings. You can set your favorite photo as the password background and even enable or disable vibration effects upon unlocking apps.