If you've locked your keys in your car, or just need to open your car up and don't have your key fob handy, you can still open the door without calling a locksmith or a lockout technician if you have the right tools and information to prove to a police officer that you're not trying to steal someone's car.
Check all doors and the boot to make sure that you can't access the interior through another avenue. The process described can be time-consuming, and if done incorrectly could lead to paint scratches in several places.
Straighten out your coat hanger or metal rod, ensuring that it is several inches longer than the distance from the top of the door frame to the location of the latch for the door.
Bend the rod in at the top to create a handle to use when manipulating the latch. Make another smaller hook at the opposite end. You may need to look at the inside of the opposite door to determine the best shape for the smaller hook.
Attach a piece of fabric or rubber from a balloon or other object to the small hook of your new unlocking device. Due to the long length of the rod and the slippery nature of metal, you will want to have some friction to keep the rod from sliding over the inside of the door.
Insert the wedge between the glass and the weather seal around the window. Most cars will be built in such a manner that you will not be able to accomplish this, in which case you will need to unlock the door and move the window from inside.
Insert the wedge at the top of the door so that a gap appears of roughly 1/2 inch. You may need to find another object to create a smaller gap before using the larger wedge or doorstop.
Manoeuvre the metal rod so that the small hook is touching your lock mechanism. Move it so that the hook actuates the lock. You may need to look at the opposite door again, or enlist the help of a friend to guide the rod while you're attempting this.
While you are legally entitled to unlock your own vehicle, the process may appear suspicious to a law enforcement officer if he sees you. Having your registration available can limit problems with opening a car window from the outside on your own.