Mattel's Sonic Slam for indoor tennis

Sonic Slam is a pair of stringless rackets that have built-in motion sensors as well as speakers so you can play with an invisible and intangible ball.

The game is all about swinging at a certain time after hearing a certain sound. Then the other player hears the same sound, and then sends it back. Sonic Slam has some other interesting games, like playing a single match against the wall. It also has an assortment of flashing lights and some cartoon sound effects.