LAS VEGAS -- Microsoft will announce tonight that Natal, a motion sensor for the Xbox video games system, will go on sale in time for the 2010 holidays.

First demonstrated at the E3 gaming conference in 2009, Natal senses gamers' gestures and motions so they can, for example, block balls in a dodgeball video game by jumping around, or play a racing game by holding an imaginary steering wheel.

Robbie Bach, president of the Entertainment and Devices division, is expected to make the announcement when he joins Chief Executive Steve Ballmer on stage during a keynote speech at the Consumer Electronics Show tonight.

"We're so excited. This comes down to our investment in natural user interface, NUI, over the last 20 years. It's this magical inflection point in technology," said Craig Beilinson, director of marketing for the entertainment division.

Beilinson said Bach is also going to announce Game Room for the online network Xbox Live. Users will be able to access old arcade games and design an online arcade room with their avatar and invite friends.

You could also go to Full Tilt Ice Cream in White Center, which has 25-cent pinball machines and the stand-up arcade games "Frogger" and "Donkey Kong." But you might have to interact with real people.

Keynote begins at 6:30 p.m. I will be livetweeting the speech, and the rest of CES, on www.twitter.com/sharonpianchan.