Gents, I need some clarification.
My keys and fobs are separate. I don't know whether the fob is aftermarket or genuine one that came with car. But it looks it.
Lately one of my fobs (the one I use all the time, the other is a tucked away spare) has been picky, when locking/unlocking. I put it down to battery.

Over the weekend , I dived into crystal clear Jamieson river. Upon exit I realised my only key and fob with me were in my pocket. The other ones were 200km away at home. I s*** my self, because the key has a small crack on the corner exposing internals (see photo below). I thought, I'll be stranded as the NATS component in the key was now water logged. Hung it up and it dried for a few hours. FOB no longer unlocked/locked the car, but the key locks/unlocks fine and car starts no issues.

This morning I thought I'd address the issue and get the key sorted out before it breaks down even more and leaves me stranded somewhere . Got battery replaced in FOB at Mint. Now works perfectly. As for the key, I went to nissan and the bloke confused the s*** out of me...
One nissan key was $250. Fob was $99. Plus programming was extra $150. And you had to get both re-programmed at once.
Ok fair enough, if thats what it costs.... But it sounded suss to me, so I walked away and went back to Mister Mint who replaced my battery in the fob earlier.

He can get a key for $100, but I'd have to take it back to nissan to program. And he says the fob has nothing to do with NATS. All the NATS stuff is in the key itself. I was also under the assumption that for FOB is only for central locking nothing else. So I don't know if the nissan bloke was pulling my middle leg.

Can someone tell me whether the transponder for NATS is in the key only or fob too ? So if i dont unlock the car with the fob, the key won't start the car?
Has anyone been through the process and can point me to a solid answer... Cheers.