After a generator is repaired, The Entity blocked the generator with the most progress for 30 seconds.  You see its white aura during this time.

Each time a generator is repaired, all windows and vault locations within 32 meters of it are blocked for all Survivors for the next 30 seconds.

Performing the Damage Generator Action on a Generator activates Oppression:

Causes up to 3 additional Generators to also start regressing.
Triggers a difficult Skill Check on all Survivors currently repairing one of those Generators.
Oppression has a cool-down of 120/100/80 seconds.

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.