Sangheili personal energy shield
From Halopedia, the Halo wiki
The Elite's armor generates a recharging energy shield which is similar to the MJOLNIR shields. This shield recharges after being depleted and can be enhanced by the Covenant's overshield technology. These shields supposedly replaced the triple-layered Elite Arm Shield in the E3 preview for Halo: Combat Evolved. These shields are a better, more efficient version of the Jackal's energy shields. There appear to be differences in the strength of the shields, and different ranks of Elites have different amounts of power and recharge capacity in their shield.
These shields have weaknesses however, as they are susceptible to damage received from plasma based weapons. We are unaware if the shield can be modified like the MJOLNIR suit, which can have it's thickness and proximity to the body altered. These shields are blue unlike their MJOLNIR equivalents. However, in Halo 2, Heretic Elites have purple shields. Unlike MJOLNIR the Elite's shields can resist low caliber munitions like that of the Assault Rifle. Sometimes the bullets bounce off the Elite's shields, but still cause damage. This is also true with the M6D Pistol, some times, on harder difficulty levels, if you shoot an Elite with the pistol and don't hit him directly, like if you hit his shoulder, the bullet may bounce off and hit the ceiling.
These shields need to be switched on in the novels so sniping with the element of surprise is more effective, but they are always on in the games.
