"It's crazy to think that soldiers of a thousand years ago wielded the spear and shield, and now, we wield the gun and an invisible shield. The shield's immortal, man."

— An Alliance marine joking to his comrade about the evolution of shielding in warfare.

The Kinetic Barrier, known colloquially as Shields and Barriers, were a form of electronic, kinetically sensitive repulsive mass effect fields designed to protect a person or object from projectiles moving at sufficient kinetic speeds so as to be deflected by the barrier. Projected from tiny emitters, kinetic barriers produce a mass effect field around the person or object that deflect small objects travelling at sufficiently high speeds, which ranges from bullets to other dangerous projectiles such as debris or fragments from a grenade. However, as kinetic barriers are only kinetically sensitive, kinetic barriers will only deflect objects that move below a certain threshold: a bullet will move fast enough that the barrier "detects" its presence, and immediately springs up a field to deflect the projectile, but elements such as fire, gas and water won't be registered by the barrier, and thus offer no protection against them. This also goes for directed energy projectiles such as plasma, which is why geth was so devastating during the Eden Prime War, as their plasma-based weapons simply bypassed the barriers of the Alliance marines who fought them. This lack of total protection however also offers its benefits: for example, a person with a kinetic barrier emitter can sit down without knocking away their chair. The kinetic barriers have limits in this regard however, as the field is only projected to a certain range beyond the body, meaning that if a gun was fired or an explosion occurred within the protective envelope, it would not be deflected: the barrier will not, for example, deflect a bullet fired from a gun that's held straight against somebody's head. To the same extent however, a kinetic barrier will not deflect an object being launched from within the envelope, allowing a user to wield a weapon and fire it without worrying about their own barriers deflecting it back at them.

Kinetic barriers in the asari cycle were first invented by the asari in 38 BCE: however, kinetic barriers as a technology has existed since the Leviathan cycle, and is a technology that has been consistently reproduced by every civilization that has come after it. As the technology for kinetic barriers evolved, so did its applications: initially built for military use and only equipped by the common ground soldier, it continued to be adapted, with larger emitters built into the hulls of starships to grant them protection, and eventually became standard issue for any spaceborne warship. Centuries would pass and the kinetic barrier would be reduced to the size of a chip, able to be strapped to a belt for a person to use without needing a suit of armor. Eventually kinetic barriers existed in all shapes and sizes, from a small chip strapped to the average citizen's belt, to being mounted on massive starships and ground vehicles. Following the Reaper War, a massive revolution in technology occurred, with new technologies popping up at a feverish pace. Among these was the energy shielding developed by the Galactic Dominion which would render kinetic barriers obsolete. Now no longer kinetically sensitive, energy shielding would deflect any object, including plasma, fire, gas...even punches, encasing the user in a layer of complete protection. By 2235 CE, energy shielding had been adopted galaxy-wide, although kinetic barriers continue to be used as a cheaper alternative for the average citizens in the centuries following and are still used to this day.