The Back to the Future Flux Capacitor Light Up Keychain shrinks down one of your favorite devices for making time travel possible and lets you hook it right on your keychain. No plutonium needed, this sucker is electrical. On/off button on the side activates the lights! Dimensions: 2" x 1 3/4" x 3/4". Batteries: 3 LR44/AG13 1.5V button cell batteries (included). Officially-licensed Back to the Future merchandise.