What is "u-force"

The U-Force is a game controller made by Brøderbund for the Nintendo Entertainment System. It employs a pair of perpendicular consumer IR sensor panels to translate the user's hand movements into controller signals.

From a print advertisement c. 1989:

Introducing U-FORCE, the revolutionary controller for your Nintendo Entertainment System. So hot, no one can touch it. Now you can feel the power without touching a thing. It's U-FORCE from Broderbund - the first and only video game controller that, without touching anything, electronically senses your every move, and reacts. There's nothing to hold, nothing to jump on, nothing to wear, U-FORCE creates a power field that responds to your every command--making you the controller. It's the most amazing accessory in video game history - and it will change the way you play video games forever. It's the challenge of the future. U-FORCE. Now nothing comes between you and the game.