James T. Kirk, a recipient of senceiver technology.
A senceiver was an experimental technology being tested by Starfleet Command in the 2260s and 2270s decades.
History and specifics[]
The senceiver was implanted inside some Federation Starfleet officers' brains, and acted as a communications medium, allowing text and visual messages to be transmitted into the person's consciousness. The use of the senceiver was somewhat controversial, with some worried that the technology could be put to use for mind control. These officers were usually of command rank or higher, and the implants allowed these officers to receive emergency messages from command inside their own minds.
When James T. Kirk was promoted to his first command, he was implanted with a senceiver. The requirement for command-level officers to have this implant was strictly secret at that time. These implants were rarely used. For example, Kirk only received two messages via his senceiver implant the entire time he had the implant. The second one was to warn of the approach of the V'Ger entity.
Starfleet kept the existence of these implants highly secret. They feared that public knowledge of the devices would lead the public to conclude that Starfleet was implanting mind control devices inside individuals.
In the year 2273, Admiral Kirk was able to receive the visual recording made of a battle between three Klingon K't'inga-class battle cruisers and the V'Ger entity. (TOS novelization: The Motion Picture)
By the 2280s, only flag officers serving planetside were required to have senceivers, and used primarily as locators rather than communication devices. Still, Doctor Leonard McCoy hesitated to use this device when trying to track down Admiral Kirk, considering it an invasion of privacy. (TOS novel: Strangers from the Sky)