Beacon tower

A beam emitter tower on Alpha Halo.

A beam emitter is a Forerunner device or a structure that, as the name implies, emits beams of energy. There are several types of beam emitters on Forerunner installations.

Description

A beam emitter on Valhalla.

Beam Emitter towers are large delta-shaped structures with a cleave down the approximate center. They fire unknown beams upwards, in the case of the Halo installations to the center, and in the case of the Ark up into space. They are likely used to transport energy for the activation process of the Halo rings or used to get rid of excess energy. It is also possible that the beams seen on Installation 04 are simulated firings of Alpha Halo.

Around Installation 00's Citadel, three Barrier Towers resembling beam emitter towers are used to project an energy barrier that surrounds the Citadel.

Appearances

Beam Emitter Towers appear in the following levels:

Halo: Combat Evolved

Halo 2

Halo 3

Halo Wars

Labyrinth

Halo: Reach

Continuous beam emitters

A Installation 08's control room as it is activated in Halo 3 level Halo.

In Installation 04's Control Room.

This type of Beam Emitter is usually seen in different types of activation structures.

The Control Rooms of the Halo installations also possess a type of Beam Emitter. Instead of a single bolts of energy, this type of beam emitter fires a continuous beam from the depths of the Control Room to the top of the structure, and into the center of the ring when the Installation is activated. In case the firing sequence is canceled, like on Delta Halo, the beam collects into a large bolt of energy, which is fired into the center of the ring.
The Ark Portal in Kenya also has this type of Beam Emitter. It's fired when the Portal is activated.
The Apex site of the Unnamed Shield World also possessed this type of Beam Emitter.
The Phase Pulse Generators on the Halo Installations are an example of this type of Beam Emitter.

Trivia

If you manage to stand at the top of the chute in which the beam shoots from, the beam can either kill you, sending you over a hundred feet in the air, or completely pass through you. When you are killed by the beam, it will say "(Player) was killed by the Guardians".
In Halo PC, the beams coming from the beam emitters will most likely kill you if you are hit by one. However, in Halo 3, the beams coming from the beam emitters (except in Valhalla) will not kill you, no matter what. This is most likely due to gameplay reasons.