Key in Public
Hi Jonny - this isn't a key in a cylinder, it is the actual key. https://www.maturemetal.com/product/security-screw/
My wife loves to flaunt her key. If she is asked about it, she doesn't say directly what it is for, but replies with something vague like the "key to her marriage" or the "key of love."
She told her sister that it's her "power key" and when she's wearing it, then she has the power to decide when I "get some." But she's never told her overtly that it goes to my chastity cage.
We have an assortment of Master locks with various colors that she matches the key to her outfit and my lock to her key. She mostly wears the pink or black key, usually on a necklace, but sometimes on an anklet.