Sentinel beam

The Sentinel Beam is a Forerunner directed energy weapon used by Sentinels. The weapon is particularly effective against small Flood outbreaks, and is efficient at stripping energy shields. Although typically integrated into the structure of a Sentinel, it can be used as a hand-held weapon if scavenged from a destroyed Sentinel.

Design details
The Sentinel Beam was designed to effectively destroy Flood biomatter, and is intended for use against minor Flood outbreaks. Although the weapon is integrated into a Sentinel's structure, its internal power supply allows it to function independently if its Sentinel is destroyed. However, when it is not hooked up to a Sentinel, its battery life is very short. The weapon projects a yellow-orange or blue beam of superheated particles, which is capable of effectively cutting through organic matter.

Two variants of the Sentinel Beam are seen: the standard yellow-orange one in the silver housing, and the more powerful blue beam, which is encased in a gold housing.

There is a battery housing on side of the weapon, which has a calibration dial on it and can be adjusted by the user.

The beams used by the Sentinels at Onyx were a golden color, with temperatures as high as 15,000 Kelvin. Although this variation of the weapon took significantly longer to charge, it is thought to have been capable of depleting a fully shielded MJOLNIR Mark V Armor suit. Furthermore, Onyx Sentinels were capable of cooperating to generate golden beams capable of destroying entire Covenant Cruisers.

Advantages
Continuous contact from a Sentinel Beam can be devastating even for armored opponents, and its ability to rapidly drain energy shields makes it an effective weapon against the Sentinels themselves. The weapon can temporarily overheat if 20% of the battery is used up in one continuous shot; the weapon vents excess heat in an attempt to counter this.

It is, obviously enough, extremely effective when used against Flood, and will cut down any form — including the vaunted Pure Forms — if aimed properly.

It possesses a decent rate of fire, amazing accuracy and range, and sustained attacks with the weapon inflict large amounts of damage. The weapon's melee attack is about as strong as that of a Rocket Launcher, and is likewise considerably slow. The melee is also capable of disintegrating a Flood combat form, although this process takes many hits and is impractical in most situations.

Disadvantage
When compared to the standard silver variant, the golden Sentinel Beam is more powerful, however it overheats more quickly and its charge depletes faster. This difference is very similar to the relationship between the Covenant Plasma Rifle and the Brute Plasma Rifle.

Changes from Halo: Combat Evolved to Halo 2

 * Like the Energy Sword and the Fuel Rod Gun, the Sentinel Beam cannot be used by players in Halo: Combat Evolved. In Halo 2, the Sentinel Beam can finally be used.

The beam makes another appearance in Halo 3, with a few visual upgrades and several technical fixes. Unlike its Halo 2 counterpart, the weapon now has virtually infinite range and fires a much stronger beam that, if held consistently on an enemy, can destroy them within seconds.

In Halo 3, the weapon does not spawn on any unaltered maps, and gametypes cannot be used to force it to spawn; it is only available in Forged map variants. This is likely due to the weapon's increased power and range, which make it devastating in Multiplayer matches.

Campaign

 * Ironically, it is a very good weapon against Sentinels in Halo 2 and 3, likely because the Forerunners didn't plan on it being used against the Sentinels themselves.
 * On the Halo 2's campaign level Quarantine Zone, provide two of your Elite allies with Sentinel Beams, and have them board the riding seats of your Spectre. Since NPCs can't run out of ammo, they make excellent weaponry. Unfortunately, further in the mission, if you manage to keep both Elites and Spectre intact to that point, you have to leave the Spectre.
 * In Halo 3, the Sentinel Beam performs greatly against the Flood, as Infection Forms will burst if they are even slightly touched by the beam. Human Flood combat forms will die instantly, though Elite and Brute forms may take longer to kill. Aim for the Infection Form embedded in their chest and you'll kill it. Pure Forms are tougher due to their evolved forms; Stalkers and Ranged Forms will die by the time the weapon overheats whereas the Tank Forms will require two long blasts to take down from the stomach.
 * In Halo 3, the Sentinel Beam is very useful for taking down a Brute's Power Armor quickly and effectively. It is also great for taking down Jackals and their shields as well as Grunts' armor, but it may overheat.

Multiplayer
The Sentinel Beam is quite rare in multiplayer games, and if available, it can be a powerful weapon in the hands of the well-trained.

Halo 2

 * This is best used in a small map like Warlock. Also good for Headlong as long as you have other more powerful weapons with you.
 * If the Sentinel Beam is the only weapon you have, conserve ammo and rely on meleeing as much as possible. It has a quick and effective melee. Only fire the weapon when your target is far away, because ammo goes fast. Melee in close quarters, and avoid deadly crossfire. Replace it as often as possible.
 * A Sentinel Beam is useful against unshielded foes, so use a grenade to take down the opponent's shields followed by a burst from the Sentinel Beam can quickly kill an opponent.

Halo 3

 * During a game of Infection, the Sentinel Beam is an effective way to rid yourself of chasing Zombie forces, but take care as to where you aim, since the beam is easy to spot and is likely to give your position away if the shot goes astray.
 * When loading up vehicles, a Sentinel Beam in the passenger seat is an incredibly deadly tool. The most flexible location is in the back seat of a Mongoose, although the passenger seat of a Warthog or Prowler is also useful and advantageous to the match. The advantage of vehicle-bound Sentinel Beams is that it can 'clothesline' foes (although this technique should not be depended on).
 * Steady shots can make the Sentinel Beam a great anti-sniper weapon. Fire at the sniper and then sweep the area. You will eventually meet your target, and they will have a difficult time evading the beam. While this technique is unlikely to kill a competent sniper, it is a good way to prevent them from using their scope.
 * The Sentinel Beam has an extremely large power consumption rate, about 5% per second, so always carry a backup weapon and try to save the Beam for emergencies.
 * The Sentinel Beam was not available in any Matchmaking playlists, until it was featured on certain map variants used in the Bungie vs World playlist and the Maption Sack playlist. Its exclusion from regular matchmaking is likely due to the weapon's power.

Trivia

 * The only way to use the Sentinel Beam in Halo: Combat Evolved engine without extensive use of the Developer Mode is to use Halo Custom Edition to acquire the Sentinel Beam involves using bump possession to attain a Sentinel and then switching back to Master Chief and have him destroy said Sentinel and exchange a weapon for the Beam. The beam is not visible from the first or second person view and if the player presses the fire button a damaging red beam will appear from the center of the screen.
 * In Halo 2, if the player throws a grenade when his/her Sentinel Beam is overheating, sometimes the animation for throwing the explosive will not appear, and a grenade will just "fly" out from the player.
 * In Halo 3, the beam appears to impact with large force, as it is able to flip an airborne Warthog with minimal effort, a feat that not even explosive weapons can achieve. This is easily witnessed during the Warthog run near the end of the game.
 * In the final level of Halo 3, a red Sentinel Beam can be found falling outside after 343 Guilty Spark is destroyed.
 * The Automated Turret in Halo 3 and the Focus Rifle in Halo: Reach fire beams that are similar to that of the Sentinel Beam.

List of appearances

 * Halo: Combat Evolved
 * Halo 2
 * Halo 3
 * Halo Wars
 * Halo: The Flood
 * Halo: Blood Line