Homing Camera

The Homing Camera (追尾カメラ) is a ball-like object that was used to track movements of competitors in the Daihaseisai.

Appearance
The device resembles a ball with queer markings all over its surface, which resemble air events and may explain how it is able to hover.

Principles
The somewhat ball-like device can levitate or float up in the air indefinitely, and move on its own, allowing it to track competitors. It has shown to have a camera, as well as some speakers and receivers, which allows it to see events unfolding, as well as give announcements and communicate with the players when necessary respectively.

The camera on the ball apparently has enough capabilities to allow it to detect a competitor who is hiding.

Daihasei Festival Arc (Railgun)
The device is first seen being deployed in the Daihaseisai, during the Balloon Hunter competition between Tokiwadai Middle School and another school. It displays its capabilities most prominently, during Kirifu Megumi's confrontation with Omoshi.

Kouzaku Mitori later takes control of several of them to give her an edge against her battle with Shirai Kuroko during the Level 6 Shift attempt on Misaka Mikoto. Uiharu Kazari was able to hack in to use Mitori's reliance on the cameras by feeding her a false image of Kuroko's death giving her time to track down Mitori's location. Since it was unknown which cameras were under her control, Uiharu hacked into every camera to pull off the deception.