This gadget in question is introduced early on in the film. After Batman has visited the scene of the first murder at Mayor Don Mitchell Jr.’s home, he goes back to his Batcave and takes contact lenses out of his eye. Clearly, the lenses have recorded everything that happened, allowing him to print out a copy of the cipher the Riddler left behind so he can analyze it at his leisure — and allowing the clever Alfred (Andy Serkis) to put his puzzling skills to the problem as well.
However, these contacts haven’t just recorded video for later analysis. They also provide information in real-time by projecting words and other intelligence onto the eyeballs of the wearer. This provides a sci-fi (and somewhat Iron Man-like) touch to Batman’s mission, while still not seeming so high-tech that it messes with the film’s sense of realism.
One Redditor pointed out that the movie did a good job of setting this up, as Batman is criticized early in the movie for staring at people. It’s revealed later that the lenses require a certain amount of time focusing on a subject to provide identification based on its facial recognition abilities, which is a good way to demonstrate the limits of his (admittedly very impressive) technology. “So the whole time Batman is actually looking at people to see their identities and making sure he’s getting good footage to check on it later,” u/monsterpoint said.
