The Tech Shield is a exotic survivor ability, and can be purchased in the token shop.
The Tech shield was nerfed about 2 hours after its release. Before its nerf, it blocked 75% of damage, granted 2 more overshields per gear strength, and dealt twice as much damage.
The Tech Shield blocks 60% of damage taken, no matter what the attack is, while dealing a small amount of damage [10 with maxed Gear Strength] to enemies within touching distance, provided the shield is active. Also, as a bonus you gain 10 Over Shields overtime just from equipping it. However, the Tech Shield slows you down while active.