As others have said, only you know your kids, although I would be less concerned with what they would like to have and more with what *you* are comfortable with in terms of freedom. Lots of folks use walkies talkies, we used a check in system. Someone else recently posted about using yellow sticky notes stuck to the mirror in their room telling where they would be and at what times.
BTW, typing in all caps is considered screaming, and although I can vouch that teenagers make you want to scream, I'm sure that's not what you intended.
Have a great cruise.
dorothy