The Digital Control Device aka Digivice. There are three types Data (blue), Vaccine (green) and Virus (red).
Features that use the yellow scanner at the back:
Can scan a card from the Digimon card game to execute Card Slash.
Can analyse nearly every Digimon encountered.
Can detect when an aggressive Digimon is nearby.
Can display a map of the current area that the Tamer is in.
Features that use the device at the top back:
Stores the Digimon's Digiegg until it hatches.
Can store the Tamer's Digimon to allow it to recover its health.
Has the ability to open Digiports.
This image is based upon kyubikudagitsune713's [link]