Another great little device is one of thoese walkie-talkies that enable you to keep in constant communication with another person up to a few miles away. I've seen it work on a great big confusing Carnival cruise ship. I've been walking around for half an hour and can't find the elevator. You're on the Lido Deck, port side. I'll come get you.
Hotels have all sorts of key systems.
The one that I most appreciated was the card key that, once you enter the room, you have to put in a slot by the door to activate the electricity. First time was sort of, uh, the word, the word . . . Ask me how many times I've lost hotel keys. Well, ahhh, I forget. . . . The butler's sole purpose is to smooth the way for you.