ISO - Draco teaches Hermione to call signet ring (it vibrates)

Looking for a fic I read where Draco teaches Hermione to call the signet ring, he may not be able to use magic- I can’t really remember. I do remember though that it vibrates, and he tells her how to use it on herself. I believe the fic is 8th year at school. He may have her call it so he can use it on her, I really can’t recall. Thank you!