It would probably be just as easy to use a plain field as a Validator for what you describe. Say you have a field named "myfield". You could then have a button with a script something like:
on click do if myfield.text ~ "the password" go[someOtherCard] end end
Or perhaps you could give the field a script and enable a button when it contains the correct text?
on change val do myButton.locked: !val~"the password" end
This thread has some additional discussion about implementing a password/search system that might be useful.