Passengers in Berlin's Friedrichstrasse underground station were recently treated to a clever use of augmented reality. In order to demonstrate the capacity of its new car, Mercedes-Benz set up a radio receiver that recognized wireless signals from car keys, letting passerby "unlock" pictures of the car on digital displays by pressing their own car's unlock button. Once they did, the screen would play a clip of the door opening and something — robots, bodybuilders, or troupes of dancers — emerging from the car. You can check out the ad, along with a quick explanation of how the underlying tech was set up, in the video below.