Armor lock

The unnamed shielding attachment is an external energy shield generator, developed by ONI's Section III R&D teams as support for the shielding system of the MJOLNIR Powered Assault Armor/Mark V.

Description
This device can temporarily enhance a SPARTAN's shield into near-invincibility, although when the shield is active, the user is unable to move. After a five-second period, the device deactivates and an Electromagnetic Pulse is released from the armor.

The use of this device is referred to as "Armor Locking".

"Armor Locking"
The device is only available for those playing SPARTANs in Halo: Reach. When performing an Armor Lock, the player is impervious to all damage, but it also renders the player immobile. Along with this, when the Armor Lock is activated, it will shed stuck Plasma Grenades and Needler rounds, Plasma Launcher rounds will be rendered harmless and rockets will be deflected. It will emit a powerful Electromagnetic Pulse when in use. The animation for Armor Lock is a SPARTAN, slamming his fist on the ground. In doing so, he starts to emit an EMP as long as the button is held or until the Armor Lock ability is over.

Armor Lock can be charged up in three stages, with each stage inflicting a stronger EMP and pushing opponents farther away. Armor Lock does restore health or shields unless someone attacks you while in armor lock. It also provides a few moments of invincibility, while making you immobile. The ability will recharge once you stop using it. A quick way to neutralize the advantage of a SPARTAN using armor-lock ability is to remain outside the EMP zone, fire one shot at him or her every once in a while to keep the SPARTAN's shields down, and then attack when he or she either released the button, or drained all of his or her stamina.