But so far there hasn't been a robot that you actually can't see. At least not without a special augmented reality vision screen.
The demo was posted by Japanese developer kidach1 on Twitter. It shows a person in a parking garage looking around with an overlay on half of their vision. Suddenly, they turn around to seemingly look at nothing, but when they pull up the overlay again, a menacing-looking droid appears.
The caption on this video reveals that this is the prototype of a developing game where the mission will be to locate and capture the hidden droid. Using GPS tracking, the droid walks around somewhere near you, completely invisible, and it's up to you to use the special vision to locate it.
To me, this is certainly the coolest robot-based ARKit game we've seen so far. Not knowing where the robot is going to show up is thrilling and interesting. There is no word so far on when this game will see the light, but in the meantime, you can support kidach1's Patreon page if you think this is a game you'd like to play.