Translation sphere

Translation spheres, also known as translator balls, were special translation devices carried by Ood who were enslaved by humanity. In order to use it, an Ood pressed a button on the sphere, and spoke into the tube, which had to be in their mouths for the sphere to work. A sphere remained permanently fixed in the mouth of its owner via this tube. The tube was linked to its owners body in the same way as their smaller hind brain once was since only enslaved Ood had translation spheres. (TV: Planet of the Ood)

These translation spheres could be clipped on the Ood's shirt when they were not holding them. (TV: The Impossible Planet / The Satan Pit, Planet of the Ood)

The Doctor acquired an Ood translation sphere at some point and kept it in the drawing room of his TARDIS. (GAME: TARDIS)

When the Eleventh Doctor, Amy and Rory arrived in the bubble universe, they met an Ood called Nephew with a broken translator sphere. When the Doctor opened it up and repaired it, the translator picked up the recorded messages of the murdered Time Lords from their Hypercubes. (TV: The Doctor's Wife)

Use as a weapon
Rebellious Ood somehow managed to turn the spheres into deadly weapons. Ood Operations had no idea how this was done, and indeed did not initially notice it, attributing deaths to heart attacks and industrial accidents.

There were two ways the Ood were seen using the sphere as a weapon. Either they threw it at the victim(s) and let it spring back and caught it, or they could simply place it on someone's forehead. The effect would be the touched area lighting up and crackling with electricity, and the human would drop to the floor, dead. (TV: The Impossible Planet / The Satan Pit, Planet of the Ood)