The Model S key fob is certainly unique looking, but I'm not sure what plans Tesla had for attaching it to one's key ring. I could not find any small key ring that would fit through the very small opening in the fob, so I came up with the following idea. Using a small piece of 20 G stranded, electrical wire (similar to telephone wire), I bent and tied a 1/4" loop through the slot in the fob. I then put a very small spot of electrical solder at the twist of the wire loop and snipped off the excess wire. A common 1/2" split key ring easy fits through my 1/4" soldered loop, and your regular key ring or chain will easily fit through the 1/2" loop. It all fits together very securely and looks good. One caution: the key fob is plastic, so be very careful not to overheat the soldering of the wire, or that will melt the plastic. The soldering should take about 2 seconds. If you are not handy with a soldering iron, a jeweler will gladly do the job using similar stranded silver wire.