- "Marine, if you run across any operational Sentry Bots, use them. Those guys pack a lot of firepower."
- ― Sergeant Kelly [src]
The Sentry Bot is a small, dog-sized security robot consisting of a robotic "head" walking on four spider-like legs. It is used in all places of Mars City in Doom 3. Each Sentry Bot is equipped with a powerful Machine Gun and a Flashlight. They were constructed by Mixom Corporation for the UAC. However, there were many problems with them. For example, a UAC employee was almost killed by a Sentry Bot because it had a system failure. Fortunately, a nearby Marine managed to disable it.
At the beginning of the game, they can be seen in the Marine HQ. One Sentry Bot will lead the player to the Mars City Underground elevator. When the demons invade the base, most of the Sentry Bots are destroyed. If you find one, it will help you fight the demons. Sentry Bots make excellent allies; their standing is about on par with the more elite demons such as the Revenant or Chaingun Commando, and they can easily mow through groups of Z-Sec soldiers or Imps. In Resurrection of Evil, however, they can be overwhelmed and destroyed by multiple Revenants, or by Hell Knights in The Lost Mission. However, in some levels, you can access another Sentry Bot if the current one becomes disabled in combat.
Sentry Bots can harm the player with friendly fire if they get between them and an enemy they are firing upon. As a result, it is advisable not to engage in close combat with enemies when escorted by a Sentry.
- Health: 300
- Attack Damage: 5 (machine gun)
- Locations: Mars City, Mars City (Revisited), Enpro Plant: Energy Processing and Storage, Communications, Erebus Level 6, Phobos Lab Sector 3
- Cheat spawn: "spawn char_sentry" (does not work) / "spawn comm1_Sentry" (working)
- Flashlight: "spawn comm1_sentry flashlight 1" (Sentry has flashlight on!)