Sorry about the double entendre, I couldn't resist.
Owning an '06 Vibe and an '06 Matrix and noticing the key fobs are very similar (except the Toyota fob has a "panic" button), I said to myself "self, I wonder if I can program one fob to control both cars?"
I hopped into the Vibe with the Toyota fob, went through the whole key inserting/door closing ritual and programmed the Toyota fob to work in the Vibe. Now I carry two keys but just one fob. If the cars are parked next to each other I can lock or unlock them simultaneously.
No, I don't get out much.
Bill