My car key has a type of bell cord, with several knots. I con't remember exactly what I did and how, but what you see is:
Monkey fist, but quadrupled instead of triple by the look of it, in reality it is 2 lines doubled.
Next I used the 4 lines to make a basic crown knot braid of 3 cm.
It is ended with what looks like a wall-crown knot, though it is hard to say (I made it 5 years ago, and I melted the ends to the knot.
My house keys, my bicycle keys, and my work keys each have their own keychain, all just a basic ring.