If you want to get the object that enters a specific area, the best way to do that would be OnTriggerEnter, with a collider specifying the area. You *can* compare an objects position with a certain Vector3, but if you want to get all objects that are within a certain threshold around that position, you would have to iterate through all objects in the scene, every frame (or at least in a sufficient subset of frames), and calculate their distance to the Vector3 specified, which is not very efficient.
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