I used to have a co-worker who carried a larg ring of keys on a key-bak until one day he was wrestling with a suspect and the kid grabbed the keys and threw them. The Key-Bak did it's job and returned the keys at full velocity to his groin, which put him out of the fight. I was laughing so hard I had trouble getting the suspect cuffed. As he (who will remain unnamed) wasn't seriously hurt it was funny, and the last time he ever carried his work keys that way.

I just don't fancy my knife comming back at me when it got knocked out of my hand. (for what its worth)

Take Care and stay safe