British English is "key ring"! I suppose we will all learn to speak American.
well, also in Romanian, the word ”breloc” is quite a neologism (from french breloque, http://www.larousse.fr/dictionnaires/francais/breloque), which hasn't much to do with a key chain or key ring, but it is more like the amulet (pendant, toy, mickey mouse, cheap jewelry, etc) that you hang around your neck on a chain, or wrist, or you can also hang on a key ring or key chain. By extrapolation, people use the term as the ring/chain itself, it is so new in the language that people don't know what to make of it... :)
There was no need to downvote Mark Fuller. I am also British, and it can be a pain for us having Duolingo set up in American English, and also that the Spanish course is in Latin American Spanish. Sorry for whingeing, but it can get to you, being marked wrong so many times when you are right.
Actually, key ring is common in America as well. Key chain is not frequently used.
I would disagree from my experience as an American who had lived in five different states, and visited more than half of them. Perhaps in your locality, ring is more common than chain, but i have rarely heard someone say "key ring"
When I try "key fob", people look at me "funny". splittongue well explains the meaning of "fob" in his comment above.