Armor lock

Armor Lock is an Armor Ability in Halo: Reach. When in this mode the player is invulnerable to all damage, but the player also cannot move. Along with this, when the Armor Lock is activated, it will shed stuck Plasma Grenades and Needler rounds. It too will emit a slight EMP when in use. Armor lock can be charged up in three stages, with each stage inflicting a stronger EMP and pushing opponents farther away.

Trivia
The animation used for a Spartan during Armor lock is the same animation used for Master Chief while covering inside the bubble shield in the first Halo 3 Trailer.