A free program for Android, by Adria Devs.

If you’re worried about exposing your PIN while you unlock your apps, you need a safer way to lock them. Now you can do that with a PIN, passcode, pattern, or fingerprint. You’ll see your passcode as the method you choose, and you can set up each app individually. You can even create a passcode that changes every minute, so no one can guess it.

And with the AppLock – Time Password (Dynamic Password) app, you can choose a PIN or pattern for each app. And you can create a personalized PIN for each app you add. This way, you can keep track of what apps need access to what data.