Its the last button on the right. You might have to check other scanners if one isn't activating the keypad. A lot of stores only have only one or two that activate. Lately I have noticed that they have been turning all of them off now through.
That doesn't make any sense. "We don't want knowledgeable customers looking up items they want to buy using numbers that are clearly listed on our website! We'd rather have them hassling employees to look in the stockroom and get games out of the case to scan!".