Notable appearances: Batman (1989), Batman Returns
It might not be the most traditional gadget, but it’s one of the most effective. The Bat Signal is the ultimate way for Commissioner Gordon to get in touch with the Dark Knight—who we’re pretty sure doesn’t have a cell phone plan. Now some interpretations of the Batman legend claim that Gordon came up with the idea of the signal—like Batman Begins—but in Tim Burton’s Batman, it's Batman himself who creates it.
The signal in Batman Returns is even more impressive because Bruce Wayne created a series of mirrors on top of Wayne Manor that instantly move into place to reflect the Bat Signal into his study whenever Gordon activates it. This alerts him to the signal even if he’s not looking out onto the Gotham skyline.