What triggers you while in chastity

I need to tell you about this. There is a colleague of mine who is good friends with both my wife and I, and she’s quite stunning. She’s begun sporting a key on a necklace that opens her filing cabinet containing important documents, yet it drives me up the wall! Whenever I notice the key swaying against its chain near her neck, my cock moves inside the cage. She remains unaware that I am confined, and while this is merely an ordinary house key, it really gets to me!