I got this off "The Art of Manliness" and it is actually pretty good.
Locking your keys in your car is one of those bone-headed moves we’re all bound to make at some point. No matter how smart or careful you are, mistakes happen. Knowing how to get back into your car without calling a locksmith is an opportunity to make up for your careless error. Depending on the type of door locks your car has, and on the tools and materials you have at your disposal, there are several methods you can try to get back into your vehicle. Below we highlight three of those methods.
The String Method
The string method only works on cars that have post-style door locks. Furthermore, it only works on post door locks that have a small knob at the top that will allow a knot to grip them. If this is your car and you’ve got some string, you’re in luck.
The Wedge and Rod Method
Most effective on newer cars that have automatic door locks or buttons along the door’s armrest, the wedge and rod method is also the most likely to damage your door if done the wrong way. Take caution when wedging the door open to not put too much pressure on the window, causing it to break.
The Hanger Method
Using a hanger is one of the most classic ways to get into your car. It’s especially effective for older cars using the method described here, but it can also be used as a rod for the wedge and rod method described above.