Notable appearance: The Dark Knight
Batman’s a busy dude, so sometimes he needs to outsource his gadget creation to Lucius Fox—Wayne Enterprise’s resident tech-geek. In The Dark Knight, Lucius created a way to have the signal emitted from everyday cell phones to be turned into a unique sonar beacon that only Batman could see, through the use of some specialized lenses. This sonar signal gave Bruce Wayne the ability to see everyone in the area of the signal, even if they were hiding in buildings or under ground.
Most famously at the end of the movie, Batman used this device for everyone's cell phone in the city, which helped him find the Joker. This device also gave the Caped Crusader the ultimate tool to potentially spy on all of the citizens of Gotham without their knowledge. It’s a morally grey area that would make Stalin proud.