If a Geoculus is successfully found, the item will be consumed and its general area will be highlighted with a blue circle. Upon entering its vicinity, a white arrow will point you towards its location. Once you get close enough, the Oculi symbol will appear and the blue highlight will disappear.
If a Geoculus is not found in any nearby regions, the item will not be consumed.
If the gadget detects nearby Geoculus (Very nearby), The item will not be consumed.
Note in Co-op: if you go to another player's world, it either appears to search for Geoculi based on what's in your world or just won't find any (and will display the animation that none are found). Since none will be found, it won't be consumed.
An exquisite stone plate that imitates a certain mysterious quality of the Geo Statues of The Seven, causing it to lead people to the location of Geoculi. Elemental Oculi represent the lost power of the Statues of The Seven - perhaps offering this-power-back to the statues also has significance for the lands that the gods watch over.