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, it will notify you and the item will not be consumed. If the gadget detects a Geoculus in a very close proximity to the player, the item will not be consumed.
Note: If you enter another player's world in Co-Op Mode, 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.