The Smart Disc weapons makes its appearance in Predator 2 and hasn’t been seen in any movie since then. This can be thrown by the City Hunter and can cut through almost anything. The disc can also return to the Predator after it has been thrown which suggests it has some form of tracking technology built in.
It’s unknown if the disc works with the auto-targeting system on the mask since the Predator wasn’t wearing his mask when he threw it. (In the video game AvP2, the disc weapon works just like the shoulder cannon and a red triangle appears on the screen when a target is close – this is not canon however). In the movie, the Predator throws it at Keyes and cuts him in half and then it returns to the Predator.
Behind-The-Scenes: The effects crew built detailed working discs that would light up and you could get good close-up shots of them. You can see some production concept art of the Smart Disc: