So Uh......(5.3 spoilers)

[Fenral]

The object Nero tossed out was the comm unit attached to his Tribunus suit (the one he speaks into in the Praetorium). This is after his speech talking about basically turning away from what he knew and pursuing the new unknown, so he basically did the equivalent of throwing his phone into the sea to quit his job. The warbly sound that follows is pretty close to the sound it makes when he starts talking to Cid through it in the Praetorium, so it's definitely the sound of someone--probably either the Ironworks or the Empire--trying to get ahold of the guy.

That particular scanner unit was modified by Unei (at some point), and she said it would guide Nero to the power he was seeking. Instead, he chucks it off a cliff, where it ends up picking something up at the bottom. The current location of that scanner is just out of bounds on the same map where we found the beacon that let the Crystal Exarch call us to the First.


It was originally meant to foreshadow Eureka, but then Eureka became something else, so they found a really roundabout way to pretend it was actually detecting something else CT related.