The Ghost Zapper is a special building in The Simpsons: Tapped Out that was released for Halloween in 2013. You can only get this item during the 2013 Halloween update through purchasing the building in the game using donuts. This item is only available for a limited time during this special update and once it expires it is unknown when it will be returning into the game.
How to Get
You must purchase this in the game using premium donuts during the Halloween update of 2013. This opportunity is only available for a limited time and may not be available another time.
You tap on the building to send a shockwave that will zap all other ghosts surrounding it.