The googoomamameter is a device that gauges the amount of "witchery" in an area. In the episode "Sky Witch," it acts up when Princess Bubblegum and Marceline pass through the Sleeping Gate Bramble on their way to Maja's house. When they encounter an illusion of Hambo, Princess Bubblegum throws the googoomamameter at it, triggering wooden stakes to thrust out of the ground underneath it.
The gold hexagonal case is small enough to fit in the hand. It opens on a hinge, revealing five holographic blue and green bars that move up and down.