Neural-inhibitor collar
From Halopedia, the Halo wiki
Neural-Inhibitor Collars are thick bands of metal which strap around the neck, stoping any neutral signals that aren't necessary for continuation of life. The UNSC tested them to capture of dangerous felons, but the technology was put aside for an unknown reason. Most likely for safety reasons.
General Graves used them when he tried to capture the Spartan-II unit "Blue Team".[1]
