Android: Locking your Android phone's screen is a matter of basic security, but Visidion AppLock takes your privacy to the next level by using facial recognition to lock specific apps on your Android phone.
Visidion AppLock is completely free. Once installed, open the app and select the specific apps on your phone that you want to lock down. You can, for example, require your face be scanned in order to open the settings, read or send SMS messages, or open your email. The app will then turn on the front-facing camera, take a quick scan of your face, and use that to lock the apps you've selected.
You can also set a password for those apps, so if someone else needs to access your phone or Visidion AppLock won't let you in, you can still enter a password to get around it. The password box only appears if the face recognition fails, so if you're using your phone, you'll never see it. Note that Visidion AppLock only secures apps on your phone, and not the phone itself.
Visidion AppLock requires an Android device with Gingerbread (2.3) or higher. The face recognition components require a front-facing camera; otherwise you can still lock individual apps by password.