Mutant Inhibitor Collars are devices created by Trask Industries. Their purpose is to prevent mutants from using their powers. While being worn, the collars sense the X-Gene, and if a mutant tries to use their abilities, it sends out a painful shock that can cause nosebleeds. The collars can be turned on and off remotely. They are used by Sentinel Services, law enforcement and Trask Industries. The collars are all connected to and controlled via a central mainframe in Washington, D.C.
Stronger mutants, especially those experiencing high emotions, are able to use their powers despite wearing the collar - albeit by exerting themselves through the pain. This was demonstrated by Polaris in rX. Due to all the collars being controlled by a central mainframe, if the mainframe experiences a virus or is damaged or destroyed, then all the collars will deactivate at once.