The Knock-In-Lock

You better hope you don't have to pound so hard that you end up setting off your car alarm, but if you're prone to losing your keys or accidentally locking yourself out of your car you may want to invest in the Knock-In-Key, a box which lets you unlock your car just by tapping on the window. But not just any old knocking, you have to set a five to twelve digit audible knock code so you car won't  automatically unlock itself when carjackers or squeegee men start banging on your window.

[Via TRFJ]