Sentry

The sentry is a protoss support unit introduced in StarCraft II available early in the game. It was previously known as the disruptor, and nullifier before deciding to name it Sentry.

Overview
Used to support zealots in light of the protoss race's diminishing population, sentries are protoss combat drones. They are capable of deploying guardian shields, decreasing the effects of ranged enemy attacks. They can also project force field barriers to stall or split up opposing forces. Sentries also have the ability to create hallucinatory images that can draw enemy fire while a real protoss strike force maneuvers into position to deliver the killing blow.

Game Unit
The sentry has a beam which does continuous damage to one target. Due to their high gas cost compared to stalkers, as well as their low HP and attack power, sentries are better being used as support units for other troops rather than frontline fighters.

Sentries are strong against s, s, and s and weak against hellions, stalkers, reapers, and s.

Sentry/stalker combinations are common in mid-game scenarios.

Abilities

 * For the terran-devised force field, see force field (terran).

Wings of Liberty
Sentries are not usable in the StarCraft II: Wings of Liberty protoss mini-campaign.

Force Field
Sentries can use Force Field to isolate enemy workers, preventing them from escaping their onslaught. Force Field also proves to be very effective for splitting forces or preventing them from passing through choke points. Melee units may be blocked with force fields and attacked with ranged units.

Guardian Shield
Guardian Shield is most effective against attackers with low base damage: s and mutalisks. Guardian Shield protects all ground and air units positioned over the horizontal circumference of the shield (where the shield joins the ground), even if a protected air unit is not visually within the "bubble" of the shield. However, the shield is centralized around the sentry, and units moving outside its area of effect no longer gain its benefits. This means that Guardian Shield is best used by keeping the sentry close to the rest of the player's forces. If the sentry is destroyed, the effects of Guardian Shield will instantly end.

The table shows the effective health for a defender protected by Guardian Shield. The figure assumes the defender has 1 base armor (as is the case with most protoss units), and defender and attacker both have 1 defense and attack upgrade. For example, the defender lasts 66% longer against marines if protected by guardian shield.

The comparisons vary only 0-2% assuming attack and defense upgrade levels remain evenly matched.

The Guardian Shield bonus is applied after the immortal's Hardened Shield. Therefore, effective health of an immortal protected by Guardian Shield is at least 125% (higher if the attacker deals <10 damage before the Guardian Shield bonus is applied).