A Med tracer was a medical device that allowed wounded soldiers to be found and rescued on the battlefield. In 3640 BBY during the battle of Kalandis Seven Corporal Amden vor Keioidian was fatally wounded and his med tracer was activated by his squad leader Sergeant Shanra Immel.
Behind the scenes
Med tracers first appeared in Alexander Freed's short story The Last Battle of Colonel Jace Malcom which was published in Star Wars Insider 137 and released on October 23, 2012.
Appearances
"The Last Battle of Colonel Jace Malcom" — Star Wars Insider 137 (reprinted in Star Wars Insider: The Fiction Collection Volume 2) (First appearance)