Discrete necklace or locket for key?

Hi! My wife and I (in our 30s) have recently gotten into chastity cages. I love it and am working on being able to wear it for longer periods. She keeps the key, and I love when she teases me with it. She has it on a ribbon right now, but expressed to me she'd like to put it on choker type necklace, maybe one with a locket large enough to fit the key so it looks discrete when we're out of the house. The key is small, exactly like one for a luggage lock. I have been unsuccessful in my searches so far, but I'm sure my limited jewelery knowledge and vocabulary are part of the issue. Does anyone know of something like this or have any ideas. Thanks!