Intercom
An intercom (or companel) was a fixed-location communicator and a user interface to the intercom system.

Primitive analog intercoms were used as early as the 20th century, at least on Earth. More advanced digital intercoms were developed later.

Although portable, hand-held communicators were available, advanced intercoms were the primary shipboard interface to person-to-person communications systems on the first starships in Starfleet and remained so through the founding of the United Federation of Planets and until the 24th century.

Intercoms were capable of being tied together for uniform ship-wide output. Both Earth Starfleet and Federation ships possessed this "public address" facility. Starship captains would initiate intraship communications by ordering a bridge officer (typically the communications officer, but also the helmsman or the navigator), to open a channel. (, et al.)

In the 22nd century, intercoms were additionally utilized by Tessic's species and Illyrians. ()

Typically, intercoms were built into walls and bulkheads or were mounted in workstations and desks. Intercoms could be voice-only or, as they developed into the 23rd century, include both voice data and visual images of the speaker. (; , et al.) The panels also included a red button which sounded red alert when necessary. (, et al.)

The armrest of a captain's chair often included a communication panel to allow a ship's CO the ability to easily communicate with the crew. (; ; , et al.)

In the deuterium mining colony operated by Tessic's species, intercoms were typically mounted on deuterium pumps. ()

By the 24th century, wearable combadges had displaced the intercom as the main shipboard communications device, although the companels are still available as a backup communication system. Intercoms were ill-remembered by 24th century natives who traveled back in time to ships still so equipped. ()

In 2371, the Amargosa observatory was still equipped with old-fashioned intercoms. ()

Appendices

Background information 
To recreate an intercom for , Doug Drexler did a detailed design schematic. (Cinefantastique, Vol. 29, Nos. 6/7, p. 78)

In scripts for , the term "companel" was used far more often than "intercom," with the script of ENT Season 2 installment  being the first to use the latter (for the unusual pump-mounted intercoms in Tessic's colony).

The Starfleet intercoms regularly featured on Star Trek: Enterprise were actually non-operational "dummy" units. They could be stuck to the walls of the Enterprise sets wherever needed and were affixed to the walls by double-stick tape. The shiny "speaker" part of each unit was of the same reflective plastic as had been used, in a more "psychedelic" fashion, to make the back wall of the transporter aboard the , as seen on . ( text commentary, ENT Season 2 DVD)

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Communications technology