The vents are a game mechanic found in FNaC2.
While the player doesn't have any direct control over the vents, animatronics can fiddle with the vents and try to enter them.
If an animatronic manages to enter a vent, the player will soon be jumpscared by them.
To defend themselves against such suprise jumpscares, the player has to monitor the cameras of the Robot Factory and use the phone in the same room as Chester or CAT, if the player sees them fiddling with the vents.
Doing so will scare the animatronic away, but the animatronic might reappear on another camera and try the same with another vent, so the player shouldn't let down their guard after scaring Chester or CAT.