Psi-emitter

"There's been a lot of secret Confederate research surrounding Ghosts and the Zerg. What we stole was a small but critical piece of the puzzle: designs for a Transplanar Psionic Waveform Emitter. The emitters broadcast the neural imprint of a Ghost, but at a much greater magnitude. These things reach across worlds."

- Sarah Kerrigan

The Transplanar Psionic Waveform Emitter, also known as a psi emitter, is a piece of terran technology. These portable machines have the uncanny ability to lure zerg to their signals. Those running the Confederate Ghost Program found that the zerg are attuned to the psychic emanations of ghosts. The emitters broadcast the neural imprint of a ghost, but at a much greater magnitude. They can reach across worlds, having a maximum range of around 10-25 light years. Numerous psi emitters in the same area appear to amplify the overall effect.

History
"It was the Confederacy that brought the zerg here! With all their weapons and all their starships and all their soldier boy marines, they wanted more power. So they built that box, not even comprehending the death it would bring with it. They thought they could control them or capture them. They had no idea what they had unleashed. And now they're just 'writing us off' as though we were some cipher on a balance sheet!"

- Merdith Jernic

The Terran Confederacy intended to use psi emitters to lure the zerg into isolated containment areas. Their plan was to use the zerg to put an end to their other rivals and be lauded as heroes for coming in and destroying the zerg. However, when activated, these emitters brought the entire Swarm to the Koprulu Sector rather than the manageable numbers the Confederacy had hoped for.

One such emitter, present on Mar Sara, was acquired by Sons of Korhal engineer Merdith Jernic. She was captured by the 417th Confederate Marine Platoon, which had been abandoned by the Confederacy, and questioned by its commander, Lieutenant L. Z. Breanne. Breanne was suspicious of Jernic's story of how she acquired the device (claiming the Sons of Korhal brought it to her), and Breanne accused her of activating it. Jernic suggested letting the zerg attack the cities, while the platoon would escape with the Sons of Korhal and the emitter. She claimed the atrocities of the Confederacy forced the rebels to use the device "against further Confederate aggression". The platoon eventually activated the emitter in order to lure the zerg towards their prepared position and away from the major cities long enough for the Sons of Korhal to evacuate the citizens of Mar Sara City. The platoon was wiped out.

Before leaving Mar Sara, Captain Jim Raynor, a new recruit to the Sons of Korhal, and a rebel team raided the Jacobs Installation in order to retrieve whatever designs or weapons schematics that they could find in the Confederate networks. They download data discs and fled

Sons of Korhal affiliate Horace Warfield was rumored to have played a role in collecting the emitter technology.

Antiga Prime
The rebels fled to the border colony of Antiga Prime. When headquarters completed analysis of the discs, shortly after rescuing and recruiting Alpha Squadron General Edmund Duke, Sons of Korhal leader Arcturus Mengsk called a meeting and had his second in command, ghost Lieutenant Sarah Kerrigan, explain that they contained designs for a psi emitter. He then had Kerrigan plant an emitter at the base camp of a large Confederate strike force which had arrived on Antiga Prime and established a base camp within their defensive perimeter. The zerg, lured by the psi emitter's signal, descended upon the unsuspecting Confederate forces and annihilated them.

Tarsonis
"The use of the psi emitter on Antiga Prime was a watershed event, a Rubicon, a point of no return. It was like the first appearance of ghosts in the Confederacy ranks, or the indiscriminate use of the Apocalypse bombs that leveled Korhal IV. It changed everything. It also changed nothing. For the average citizen caught between the rebels and the Confederates, and the Confederates caught between the Zerg and the Protoss, the war was still as deadly as ever. More planets would vaporize under the Protoss's weapons and more humans would be swallowed by the Zerg hives. Yet after the swarming of Antiga Prime, there was hope for the rebels. Now, at least, we had a weapon. And like the damn fool humans we were, we could not resist using it."

- Michael Liberty

Mengsk's forces traveled to the Confederate capital world of Tarsonis and had General Edmund Duke's Alpha Squadron plant emitters there, over the strong objections of Jim Raynor and Sarah Kerrigan. The combined power of the psi emitters lured billions of zerg to Tarsonis. They overran the Confederacy's defenses and laid waste to Tarsonis' major cities and industrial centers.

The Brood War
During the, Arcturus Mengsk, now emperor of the Terran Dominion, was deposed by the United Earth Directorate. The UED later assembled a Psi Disrupter on the world of Braxis, which severely hampered Infested Kerrigan's control over her zerg forces.

Mengsk was rescued by Raynor and brought to Kerrigan's Fortress on Tarsonis. She needed his psi emitters to gather up enough zerg to destroy the Psi Disrupter and confront the UED. On Braxis, Raynor's Raiders destroyed the Disrupter's primary power generator. With the Disrupter's power cut, the emitter, carried by one of Mengsk's SCVs, was able to get the attention of renegade zerg near it, allowing Kerrigan to assert direct control over them and destroy the Psi Disrupter.

The Second Great War
No record of emitters being used in the Second Great War exist.

The Terran Dominion launched a salvage operation on Tarsonis, intending to gather lost Confederate technology. Raynor's Raiders attacked this expedition, making off with an old adjutant with knowledge of the Battle of New Gettysburg. After decrypting the adjutant, Jim Raynor listened to its transmissions&mdash;Arcturus Mengsk giving the order to use the emitters to General Edmund Duke, over the objections of Raynor and Sarah Kerrigan.

Raynor's Raiders eventually took control of UNN long enough to disperse the information throughout the Dominion, weakening Mengsk's rule.