"Warning when targeted off-screen, and detect enemy explosive equipment." - Description before Divisions Overhaul
Instincts is a combination of the Engineer/SitRep perk from previous titles as well as the Perception trait from Infinite Warfare, allowing players to see enemy equipment through walls as well as being notified by the sides of the player's HUD turning yellow when an enemy not in the player's view targets them.
As of the Divisions Overhaul , Instincts now makes the player immune to Shellshock and tactical equipment.
The HUD turning yellow does not function in competitive play.
Division overlap: Armored II already grants "immune to shellshock and tactical equipment."