Jewelry Options for Carrying the Key?

As I noted in a previous discussion, my wife has agreed to actively get involved with my chastity setup. One question on my mind is whether she should carry the key herself. I suspect she won’t wear it out where everyone can see, mainly because she’d prefer not to have to explain it to people who might notice.

Has anyone come across a good way around this? I’m considering some kind of locket that would be big enough for the key. Does such an item exist?