In Starfleet, the combadge replaced standalone communicators in the early 24th century. (TNG: "Yesterday's Enterprise", "Family") Similar devices are used by other organizations, including the Bajoran Militia. (Star Trek: Deep Space Nine) In Starfleet, the combadge is worn on the left breast of the person's uniform, whereas the Bajoran Militia's combadge is worn on the right breast of the uniform. They are activated by tapping them once and deactivated by tapping them twice. (DS9: "Move Along Home", "Past Tense, Part II")
Combadges are used for on board ship communication with other Starfleet personnel when using the internal communication system is not possible or impractical, for accessing the onboard computer when not in an area that the computer is monitoring, for ship-to-shore communications and for direct communication to another combadge. Combadges are configured to act as universal translators. (DS9: "For the Uniform"; VOY: "Threshold", "The 37's", "Investigations")
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 can be opened for maintenance purposes or to be used as a beacon. (TNG: "Brothers"; VOY: "Coda")
In emergency situations, a combadge can be modified for use in other applications. It can be converted into a subspace distress beacon, or the tiny power cell can be extracted for other uses. (DS9: "Rocks and Shoals") Lieutenant Worf used it to power a home-made 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 is ever cracked, an emergency distress signal is emitted, mainly to help searchers locate victims. (TNG: "A Fistful of Datas"; VOY: "Time and Again") The Starfleet combadge can be deactivated by tapping it twice in rapid succession. (TNG: "The Game"; DS9: "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")
As a symbol of loss of membership in Starfleet, personnel that have resigned or have been relieved of duty must turn in their combadges. Additionally, personnel confined to a holding cell are not permitted to retain their combadges during their confinement. (DS9: "Paradise Lost", "Inquisition"; VOY: "Thirty Days") Taking off one's combadge constitutes taking off one's uniform. (TNG: "Redemption", "Journey's End"; DS9: "Tacking Into the Wind", "Inter Arma Enim Silent Leges")
Combadges can be used by the transporter as a way to lock on to any Starfleet personnel; more generally, the transporter can 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: "Tattoo", "Investigations"; 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")
The Starfleet insignia pin first used in Star Trek II: The Wrath of Khan would later become 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 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 appears 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 Time".
There have been three possible future combadges used in Star Trek:
- In TNG: "Future Imperfect" the combadge comprised the delta shield and rectangular strips behind it signifying rank, doing away with rank pips; while in TNG: "Parallels" the same combadge is seen again alongside rank pips.
- The second future combadge seen comprises a delta shield outline backed by two vertical gold quadrangles. 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".