Teh FDR and CVR have an electronic sonic locator beacon that is activated when it contacts salt water. You would have to be quite close to hear the chirp. I would guess no more that a hundred yards or so.
There should be an ELT in the rafts onboard. They are tracked by satellites - but not sure if they need to be manually located or are automatically engaged when hitting water. This is just weird to me.
If the entire plane was hijacked and landed somewhere else, or if it landed in the water or hit a mountain in the middle of the ocean, it should have been located by now. Unless, Airport ‘77 style, it is intact at the bottom of the ocean.