I am not sure what I think of this but it goes to show you someone somewhere will think up an innovative solution to any common problem. This is a simple product that will let you get in your car after you lock the keys inside. Knock-In-Key is made in Germany and it unlocks your car when you knock on the window in the proper code. Just don’t let anyone see you do it.
The product link in the source article is not working at the time of this posting.