This is the wireless remote (model ARMTE-001) for all GoPro models. This is a used, OEM part.
GoPro Smart Remote
A three button long range remote for some GoPro camera models.
GoPro's cameras, often used in action video photography, are compact, lightweight, and have many accessories allowing them to be mounted on individuals or vehicles. The cameras capture still photos or video in HD through a wide-angle lens.