Making use of the passcode screen in apps

I'm new to IOS programming - please keep that in mind.

I've come across several apps which perform some action when the wrong passcode is entered into the passcode screen. For example some apps take a photo and do something with it. What is the best way to work with the data entered into the passcode screen?

Please note, that I am talking about the main passcode screen which the user has set themselves (not a custom passcode screen developed in the app).

I will be grateful if you can point me in the right direction.

I've never heard of such apps. Please post some names.

I would think that even if such a thing is possible that security features within iOS and the passcode screen would prevent you from seeing the data entered into the passcode screen because that is a password. The system password at that.