In Starfleet, the combadge replaced standalone communicators in the early 24th century. (TNG: "Yesterday's Enterprise", "Family") 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, whereas the Bajoran Militia's combadge was worn on the right breast of the uniform. They were activated by tapping them once and deactivated by tapping them twice. (Star Trek: Deep Space Nine; TNG: "The Game"; DS9: "Move Along Home", "Past Tense, Part II") (Note: the EMH of 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") A Bajoran combadge is capable of recording logs such as that of the chief of security. (DS9: "The Ascent")
The Starfleet combadge was a crystalline composite of gold, microfilament, silicon, beryllium, and carbon-70. (TNG: "The Last Outpost", "Time's Arrow"; VOY: "Hope and Fear") Due to the size of the combadge, its working range was limited to five hundred kilometers, although a starship could boost the signal to bridge larger distances. (TNG: "11001001") The combadge could be opened for maintenance purposes or to be used as a beacon. (TNG: "Brothers"; VOY: "Coda") A combadge could also contact or be reached by a starship even if it was traveling at warp speed. (TNG: "The Schizoid Man"; VOY: "Resolutions")
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") Lieutenant Worf used it to power a homemade field generator for several seconds. (TNG: "A Fistful of Datas") In 2374, Captain Kathryn Janeway of the USS Voyager was able to modify Seven of Nine's Borg implants to escape the brig of the USS Dauntless using pieces of her combadge. (VOY: "Hope and Fear") If the casing of the combadge was ever cracked, an emergency distress signal was emitted, mainly to help searchers locate victims. (TNG: "A Fistful of Datas"; VOY: "Time and Again") Combadges, when destroyed by an electrical force, could cause damage to the wearer's clothing. (TNG: "Thine Own Self")
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") Taking off one's combadge constituted taking off one's uniform. (TNG: "Redemption", "Journey's End"; DS9: "Tacking Into the Wind", "Inter Arma Enim Silent Leges")
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") When Ferengi briefly took over the Enterprise in 2369, they were captured by attaching combadges to them and using the badges to beam them into a secured transporter room. (TNG: "Rascals") Commander Benjamin Sisko used his combadge to beam the embryonic lifeform off Deep Space 9 into space in 2369. (DS9: "Q-Less")
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"), Henry Starling confiscated the combadge of Captain Kathryn Janeway and the holographic combadge of The Doctor in 1996 (VOY: "Future's End" and VOY: "Future's End, Part II") and the combadges of Commander Benjamin Sisko and Dr. Julian Bashir were stolen while they were incapacitated on the streets of San Francisco in 2024. (DS9: "Past Tense, Part I")
The Starfleet insignia pin first used in Star Trek II: The Wrath of Khan later became a combadge, as Lieutenant Richard Castillo can been 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 episode "The Search, Part I", before being used continually in the series and Star Trek: Voyager. It also appeared in the four The Next Generation movies.
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".
- 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".