Here's a neat trick that let's you re-program one key fob to unlock all your cars. It's like a universal remote, but for your car.
In order to re-program the keyfob, you'll have to follow the instructions specific for your car (find them here). There's methods for GM, Ford, Dodge, Toyota and Nissan vehicles but here's how to program Chevy cars:
We'd imagine the best scenario for this is if you park your cars in a garage. Because if your cars are on the street, you might end up leaving one car unlocked while driving the other away. [Filear via Hack a Day]