After a Survivor loses a health state, Gearhead activates.

While Gearhead is active, the next time a Survivor completes a Great Skill Check while repairing, the perk deactivates and their aura is revealed to you for 10 seconds.

The Auras of regressing Generators are highlighted in white.

If the Regression progress is interrupted on a Generator, its Aura will be highlighted in yellow for 8/12/16 seconds.
Surveillance increases the audible range of Survivors Generator-repairing noises by 8 meters.

While carrying a Survivor you benefit from the following effects:

Decreases Wiggle effects, which cause you to strafe sideways, by 75 percent.
Increases Wiggle duration by 4/8/12 percent.

You become obsessed with one Survivor.  Your Obsession gains a 33percent action speed bonus to unhooking and healing other Survivors.  Each time you hook a Survivor other than the Obsession, if the Obsession is alive, gain a token.  If the Obsession is alive, all Survivors who are not the Obsession get 3percent penalty to repair, healing and sabotage speeds for each token.

Survivors within your Terror Radius have a 50percent penalty to healing progression speed, and healing Skill Checks move 50percent faster.

At the start of the Trial, 4 random Hooks are changed into Scourge Hooks:

The Auras of Scourge Hooks are revealed to you in white.
Each time a Survivor is hooked on a Scourge Hook, the following effects apply:

The Generator with the most Progression explodes, instantly losing 9/12/15 percent of its Progression and starting to regress.
Survivors repairing that Generator will scream, but not reveal their location.