A Tallus is a communications device, used by the Timebreakers to communicate with their groups of dimension-hoppers Exiles and Weapon X.

It is usually worn by the leader of the group. Only the wearer of the Tallus can communicate using it. Tallus communication is usually vocal, but it can also be used to manifest holographic projections which can be seen by the wearer. The Exiles' Tallus has been worn by Blink, Mimic and currently Sabretooth.  The Weapon X Tallus has been worn by Sabretooth and then Gambit before the group was exterminated.

Now that the Exiles is in charge over themselves it's used in communication between Heather Hudson and the group.

The Tallus was shown to be somewhat bound to its wearer. This was exhibited when Hyperion ripped off Gambit's arm to get the Weapon X'ers Tallus, but it reappeared on his other arm.