It is presumably a Bluetooth earpiece connected to the player's phone. It is used by protagonists to communicate with one another during Heists.
It is a cosmetic item with no practical usefulness over the default earpiece provided in the heists.
When the player talks when using a mic and the earpiece on, a blue light will flash on the side of the earpiece.
Grand Theft Auto V
The earpiece is automatically worn by protagonists during heist setup missions, and heists. It is also worn during various missions to allow the protagonists to communicate. It is an integral part of the Scuba Gear outfit, though it can only be seen by removing the top part of the outfit through a glitch.
The earpiece was introduced as a purchasable item in the Heists Update.
There are 3 different looking ear pieces that are in the heist gear section of Ammu-Nation. The LCD model is unlocked for purchase after completing the The Fleeca Job, while the red and gray models are available prior to completing any heist mission.
- LCD Earpiece $1500
- Red Earpiece $1350
- Gray Earpiece $1200
- The LCD Earpiece appears to be the same as in No. 3.