Personal Energy Shields are used by Jackals (Kig-yars) for protection from enemy fire. Worn on the forearm, they create a barrier that can deflect any solid projectile weapon except rockets.
Damage
Grenade Damage
It should be noted that grenades, even though deflected by the shield, can still explode and collapse the shield if detonated nearby.The shield reflects it's current charge by changing color gradually from its original color to red before it deactivates completely.
Plasma Weapons
Energy-based weapons can penetrate the shield and can even collapse the shield altogether. The MJOLNIR armor's shield was devised by reverse-engineering the Jackal shields, and it was later improved upon it to make it much more efficient.
Conventional Weapons
For some unknown reason, some of the conventional weapons can penetrate the shields if they are fired continuously. The Assault Rifle rounds can be seen bouncing off the surface of the shield, although they eventually cause the Jackal to flinch and momentarily lower its shield, allowing the rest of the Assault Rifle magazine's bullets to eliminate the Jackal.
Melee
The most effective and efficient way to kill a Jackal is with a melee attack. A direct hit to the shield will often knock it backwards into the Jackal, sending a power surge through the Jackal's body and killing it. However, on Heroic and Legendary, it will often take more than one attack. Similar to most enemies, Jackals flinch when hit with a melee attack.
Halo 2 changes
In Halo 2, the shield appears to have been weakened. It is now possible, but difficult, to bring down a shield with projectile weaponry, and a sniper round to the central dot will collapse it and stun the Jackal. However, the shield now provides the Jackals with limited melee protection.
Trivia
In the first Teaser of Halo: Combat Evolved a group of marines inside a forerunner complex engage with a major elite with a triple-layered personal arm shield similar to the jackal's.