Ghost Zapper is a device invented by Max Thunderman to detect the presence of ghosts and blast away ghosts powers.
Max revealed the Ghost Zapper to Phoebe and Taylor Hathaway while in New Orleans in Haunted Thundermans so that they can use it to defeat the Green Ghoul. He explained how it works to detect ghosts but Phoebe and Taylor didn't believe him at first because Miles and Louie kept interfering. He later sneaked out with the device to Chad's party to help catch and defeat the Green Ghoul and it almost detected Chad.
Max tried to zap the Green Ghoul with the Ghost Zapper but Green Ghoul used Phoebe's Telekinesis to throw it away and destroy it.