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The Hazardous Environment Combat Unit Sentry Gun, commonly referred to as the HECU Sentry Gun, is a fully autonomous weapon featured in Half-Life and its expansions. Sentry Guns are commonly used by the HECU, and Black Ops, to guard areas of strategic value.

They share some aspects of their design with the newer model seen in the sequel, Half-Life 2, including a tripod base and a tall, narrow body.


The sentry gun consists of a powerful machine gun built onto a tripod, mounted on a turntable unit allowing it a 360 degree field of view. Unlike its successor, which has a limited field of view.

Gordon Freeman encounters a Sentry Gun, for the first time, in the chapter "We've Got Hostiles". They were left behind, by the HECU, to guard areas after they have entered the facility.

Some of these guns relied upon an independent laser sensor to detect targets while others were deployed, without one.

Once an enemy has tripped the beam, was detected automatically, by contact, firing close (GoldSrc only) or simply damaging it then it activates, accompanied with a high pitched whine, and shoots at the sighted target.

Once alerted, the sentry would remain that way for a short time, and made a steady beeping sound as it scanned for targets while, before sinking back into its docile, standby, mode.

Despite its comical appearance, these guns were in fact rather resilient to gunfire and are difficult to knock over but any sufficient type of damage will knock them over, with explosives being the most effective tactic like grenades, though this can be hard to use.

The PlayStation 2 port included a variant, encountered later on, which attacked via motion detection. These had a red light to indicate this.

HECU Sentry Decay

Half-Life: Decay model.


Sentry Guns are powerful enemies but they do not move at all.

When encountering one stepping back and considering tactics is advised. Looking for a way around it or destroying it with explosives is a good move.

Since Half-Life's GoldSrc engine lacks a robust physics system, Sentry Guns simply fall over once they've taken a set amount of damage but can take a considerable amount of damage so opt for hard-hitting attacks such as: a well-placed Colt Python shot, a Shotgun double-blast, or explosives like: Grenades, Satchel Charges, or the RPG.

Keep an eye out for their laser sensors and avoid tripping them. Doing so eliminates the threat entirely; However, these tactics may change when playing Half-Life: Source because of the upgraded physics engine (although like their GoldSrc variants, they are destroyed when damaged enough).


  • Unlike the ceiling counterpart, these Sentry Guns do not go into standby mode and retract into its body if there are no targets in range. The only way to disable the turret is through the use of explosives, gunfire or a crowbar, as they do not have switches to deactivate them. However, in Half-Life: Source, it possible to disable these turrets by using the console command "ent_fire monster_sentry deactivate".
  • The HECU Sentry Gun shares its firing sounds with the MP5. In fact, if the Half-life: HD pack is installed, the M4 Carbine sounds are used for the sentry gun.

List of appearances

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