Special key killswitch

I remember a while ago someone posted a special key-type switch that had no duplicates, each unit was unique. It wasn't an ordinary key like for the doors or a house, it was circular with a unique design on the inside to match the other connector, which would enable the switch. I know Turkish bought one and showed it to me in person and I'd like to get one. Anybody remember what I'm talking about/have a link?