Similar devices were used by other organizations, including the Bajoran Militia. In Starfleet, the combadge was worn on the left breast of the person's uniform, while the Bajoran combadge was worn on the right breast of the uniform.
A user activated their combadge by tapping it once, and tapped it twice to deactivate it. (Star Trek: Deep Space Nine; TNG: "The Game"; DS9: "Move Along Home", "Past Tense, Part II") (Note: the EMH of the USS Voyager used this technique not to deactivate his combadge, but to gain the attention of the ship's crew.) (VOY: "Caretaker")
Combadges were used for on-board ship communication with other Starfleet personnel when using the internal communication system was impossible or impractical, for accessing the on-board computer when not in an area that the computer is monitoring, for ship-to-shore communications, and for direct communication to another combadge. Combadges were configured to act as universal translators. (DS9: "For the Uniform"; VOY: "The Cloud", "The 37's", "Investigations")
Starfleet combadges silently provided identification to starship computers. For example, when a person wearing a combadge accessed a certain console, the computer logged the individual's identification to that access. (TNG: "The Drumhead")
In emergency situations, a combadge could be modified for use in other applications. It could be converted into a subspace distress beacon, or the tiny power cell could be extracted for other uses. (DS9: "Rocks and Shoals")
As a symbol of loss of membership in Starfleet, personnel that had resigned or had been relieved of duty were required to turn in their combadges. Additionally, personnel confined to a brig were not permitted to retain their combadges during their confinement. (TNG: "Redemption", "Journey's End"; DS9: "Paradise Lost", "Inquisition"; VOY: "Thirty Days")
Combadges could be used by the transporter as a way to lock on to Starfleet personnel; more generally, the transporter could lock onto any person or object with a combadge attached or nearby, thus making transport faster and more accurate. Chief Engineer Geordi La Forge used his combadge to allow the transporter to beam off an explosive device that the Ansata terrorists planted on the USS Enterprise-D during their mission on Rutia IV. (VOY: "Caretaker", "Tattoo", "Investigations", "The Chute"; TNG: "Justice", "The High Ground")
At least five combadges have been left by Starfleet personnel on Earth centuries before they were invented; Lieutenant Commander Data sold his combadge to Frederick La Rouque for three dollars in the year 1893 to buy his way into a poker game. (TNG: "Time's Arrow")
By 2399, Cristóbal Rios, the captain of the civilian freighter La Sirena, had access to smaller combadges, called comm pins, in the shape of his ship's personalized mermaid emblem. When necessary, Rios provided them to his passengers. (PIC: "Absolute Candor", "The Impossible Box", "Nepenthe", "Et in Arcadia Ego, Part 2")
After Jean-Luc Picard used a spatial trajector to escape from the Artifact to Nepenthe, which would normally be a few days' travel at maximum warp, his comm pin couldn't reach Rios aboard La Sirena until they were within range. (PIC: "Nepenthe")
The Starfleet insignia pin first used in Star Trek II: The Wrath of Khan later became a combadge, as Lieutenant Richard Castillo can be seen pressing his and speaking into it in TNG: "Yesterday's Enterprise". The combadge with the rectangular back was designed for Star Trek Generations and first seen in the Star Trek: Deep Space Nine third season premiere episode "The Search, Part I", before being used continually in the series and Star Trek: Voyager. It also appeared in the four Next Generation movies and in episodes of Star Trek: Picard.
When the combadge first appeared in TNG, it appeared to be larger than the prop used in later seasons. It was also referred to as a communicator rather than a combadge by Beverly Crusher in TNG: "The Naked Now" and "Remember Me".
There have been three possible future combadges used in Star Trek:
- In TNG: "Future Imperfect" the combadge used in the false future comprised the delta shield and rectangular strips behind it signifying rank, doing away with rank pips; while in TNG: "Parallels" the same combadge was seen again alongside rank pips. The backing strips were colored either gold, silver, or black depending on the rank of the wearer; admiralty had a starred gold delta with silver backing strips.
- The second future combadge seen comprised a delta shield outline backed by two vertical gold quadrangles, used as early as an alternate 2390. This badge has been seen in TNG: "All Good Things...", DS9: "The Visitor", VOY: "Timeless", and VOY: "Endgame". A very similar style was later made canon in Star Trek: Picard.
- Also seen in Voyager is a 29th century combadge. This is a "winged" arrowhead, similar in style to the insignia found on a 24th century starship hull. It has been seen in the episodes VOY: "Future's End", "Future's End, Part II", and "Relativity".