Sentry

The sentry is a protoss support unit introduced in StarCraft II available early in the game. It was known as the nullifier and then as the disruptor during development.

Overview
Used to support zealots in light of the protoss race's diminishing population, sentries are protoss combat drones. Sentries employ a disruption beam to attack their enemies, and offer protection through guardian shields.

Sentries can also project force field barriers to stall or split up opposing forces. This is done by turning bursts of energy into a small, impenetrable barrier to hinder, block, or funnel the advance of enemy troops. While creatures or machines of prodigious size can shatter the cohesion of these translucent force fields, ordinary soldiers and vehicles become fodder to protoss ranged weapons.

Sentries also have the ability to create hallucinatory images through an in-built holo-projector. These holograms can draw enemy fire while a real protoss strike force maneuvers into position to deliver the killing blow. These hallucinations are composed of solid light and are three-dimensional, able to mimic protoss warriors, vehicles, and constructs. Each replica, while limited in duration, is able to withstand some degree of punishment. The purpose of these life-like images is twofold: making the enemies of the protoss believe they’re fighting a much larger force than anticipated, and protecting protoss lives.

By 2506, some sentries were being outfitted with portable shield batteries to better sustain the lives of protoss warriors in battle.

Sentries had also been incorporated into the Tal'darim arsenal by 2504 and by the End War, they had developed their own variant. Nevertheless, some were left mostly unchanged, allowing for a varied array of robotic support and a certain degree of misdirection.

Game Unit
The sentry has a beam which does continuous damage to one target. Their high gas cost relative to their low HP and attack power, delgates sentries 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.

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

Upgrades and Abilities

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

Legacy of the Void
In Whispers of Oblivion, the sentry gains a Shield Recharge ability, that functions similarly to the heal ability of the medic, restoring shields to a nearby protoss unit at an energy cost. The sentry cannot attack while using Shield Recharge. In the Legacy of the Void campaign, the sentry lacks Force Field, but the base sentries found in "Forbidden Weapon" have the Shield Recharge ability. The Aiur sentry can use Double Shield Recharge, allowing them to restore shields to two units.

The player may choose the energizer or havoc as sentry variants in the Legacy of the Void campaign. The sentry acts as a purely defensive support unit between Guardian Shield and Double Shield Restore, whereas the energizer and havoc can support the player's armies with more offensive-based abilities.

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.
 * Table:

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).

Variants

 * Conservator (Purifier)
 * Energizer (Purifier)
 * Havoc (Tal'darim)