Thank you to everyone for your answers. I will just carry the AAA card and leave it in a draw! It won't be a big loss or security issue. I know we used this scan card method once, but would not want to have to carry a "card" around just to open the safe!
Marnie, although I understand your issue with crew & security with one's sign & sail card, I certainly have never had nor heard of any one dishonestly using someone else's card. I hope this has never happened to you. It pays to check your account too during your cruise just in case an erroneous charge is applied. Pursers usually have no problem removing the charge.