Sentry

In Quake 4, the Sentry is a yellow floating Strogg designed to protect key facilities, such as the Nexus. First encountered in Nexus Hub Tunnels, the Sentry consists of a limbless, oval-shaped body with a standard Strogg head on top, and is armed with a pair of Machine Guns for "arms". At the bottom of the Sentry is a container of green liquid in which a small, humanoid, fetus-shaped creature lies.

Combat Characteristics
Sentries float through the air while firing at targets with their twin machine guns. They are fairly slow moving, although they can abruptly dodge sideways several feet to avoid gunfire or slow moving projectiles such as rockets. They are usually encountered in swarms of 2 to 4 at a time. They only appear in certain specific areas, such as the Nexus Hub Tunnels and Nexus Hub, or the main data shaft in Data Processing Security, but are encountered quite frequently in the few areas in which they do appear. They are relatively low-end "cannon fodder" enemies, and can be killed with several machine gun bullets or one or two shotgun blasts. Hyperblaster or unguided Nailgun are not recommended, due to their good agility. The Lightning Gun is perfect for taking them out quickly.

Although weak, Sentries can be very annoying since their machine guns are hitscan weapons and thus cannot be dodged even from a distance. Also, despite having very weak bullets, their full-auto rate of fire and good accuracy can chip away your health and armor at a decent pace. Taking cover from their attacks is very important when fighting them.

Strategies

 * Sentries are quite easy to destroy if you use the right weapons and try to aim for the bowl, as all attacks on it will do double damage to the Sentry. From far away, the Machine Gun can destroy them. Up close, the Shotgun can tear them apart in one to three shots. Do not use projectile-firing weapons, as Sentries can quickly dodge them, no matter how fast the projectile is. The most effective weapon against them is Lightning Gun, Machine Gun is another good choice before the player get more powerful weapons.
 * A Sentry's attack comprises a series of short bursts from its machinegun, with a pause between each burst. With careful timing, the player may be able to take cover during its firing burst, and peek out to take a shot during its pauses before taking cover again.


 * With other enemies, the Sentry should be taken out first. Even though its Machine Guns do low damage, they will distract you long enough for stronger enemies to get a few hits on you. Also you need to keep in mind that the Sentries don't fight alone, there will be more after you meet one.


 * If you have teammates around, kill Sentries quickly, although they can deal low amount of damage, their Machine Guns are fast and lethally accurate. The death of the teammate usually means game over. So try to prevent it.
 * Unlike most enemies, a Sentry will not open a door to pursue you if you have retreated to another room.

Trivia

 * It is possibly that Sentry is the replacement of the Technician from Quake II.