Long-range communication device

The long-range communication device is a two-way communication device which creates a neural link between the users on each end, swapping their minds into each other's bodies. It was originally created by the Alterans millions of years ago, before they left their home galaxy. A variant of the original was developed by the Tau'ri sometime around 2009.

Overview
The long-range communication device is used in conjunction with the long-range communication stones. When the stones are attached to the device, they create a link with the nearest active communication stone, allowing the user to take control of the person to whom the stone is linked and vice versa. As long as the link is active, the user controls the recipient's body as if it were there own.

The device, thus far, has no known limit to its range; it can function seamlessly over billions of light years. However, it appears to be unable to establish a two-way link over intergalactic distances without the aid of a second communication device on the other end. For example, when Daniel Jackson and Vala Mal Doran used one to connect to the Ori galaxy, the couple they connected were not switched in return until a second device was briefly engaged; when it was disabled, the connection back to Earth was severed. Conversely, a communication device activated by Neeva Casol in the Pegasus galaxy was to create a two-way link between her and Jennifer Keller, despite Keller not having used a communication device in return.

Once a link is formed between two individuals, it cannot be severed until the stones are removed or power to one or both devices is cut off. The Alteran version of this device will maintain a one-way connection without a companion device, while the Tau'ri version will disable the connection on both ends if either side loses power.

In cases where a one-way link is formed, the device establishes a physiological link as well as a mental one, causing the user's body to experience the stresses of the recipient's body. Thus, if a person dies while connected to another body, their original body dies as well; stressful situations have a similar transfer effect. When a two-way link is formed, however, neither side seems to be aware of what the other is experiencing. For instance, if a person were to become intoxicated while the device is active, they would be affecting the host body of their partner; if the device were to be deactivated or disrupted while that person is intoxicated, the user would find him/herself sober in the original body, leaving the other user to feel the effects of intoxication. The Tau'ri are not sure if death is still a problem in this case, but consider it a risk.

Daniel Jackson believed that the device was able to translate from Ancient to English based on his first experience with it, though later events show that the Ori followers whom they communicated with speak English. When Everett Young used the device and swapped with a blue alien, he could not comprehend their language, which uses clicks and screeches, nor could he communicate in his own tongue.

Original Alteran device
The original Alteran long-range communication device has a hemisphere-shaped based about two feet in diameter with a crystalline spire coming from the center. There are twelve communication stone slots spaced equally around the base. When active, the spire turns blue. While the specifics of the device is unknown, what is known is that the device draws power from subspace. Once activated, the device is impossible to shut off; it has no "off switch" and any stones attached to it are locked in place. The only known method the Tau'ri have for disabling the link is to destroy the device. A Prior has been shown to be able to deactivate the device without the need for violence.

History
The first encounter the Tau'ri had with a device of this nature was discovered on Avalon in Merlin's vault. Daniel Jackson and Vala Mal Doran used it in hopes of meeting non-ascended Ancients living in another galaxy. Instead, they linked to Harrid and Sallis, heretics who had discovered a similar device outside Ver Eger. The device found in Avalon was destroyed when Cameron Mitchell and Teal'c threw it into the kawoosh of an activating Stargate. The device in Ver Eger was taken to Celestis to be destroyed, but Seevis' contacts in Celestis smuggled it out to Ver Isca before that could happen. Vala, while stranded in the Ori home galaxy, used it to link to Daniel and warn Earth of the impending Ori invasion; however, the device was rendered useless when Tomin shot it with his staff weapon.

In 2008, the Atlantis Expedition had an encounter with one of these devices. Neeva Casol activated one while stealing artifacts from a village, switching with Jennifer Keller, who was the last person to touch the related communication stone in Janus' lab. To restore them both to their proper bodies, Ronon Dex shot the device, disabling it.

Ori long-range communication
Though the Ori have not been shown to build a physical version of the long-range communication device, a Prior has shown to be able to duplicate the effect using their powers (likely in conjunction with their staff). A prior in the Milky Way demonstrated this with Gerak, bringing both himself and Gerak to Celestis, whereupon Gerak was converted into a Prior himself. It's not shown if their bodies were being controlled by someone else during the exchange.

Tau'ri device
The Tau'ri, despite not understanding the technology completely, have managed to construct their own version of the device. This variant is a much smaller and box-shaped. The top of the device has a flat panel with five intersecting rings, where the stones can be placed. When a communication stone (which appears to be the same stone used in the original device) is placed in one of the five rings, the panel lights up and the link is established.

The Tau'ri version of the device has the advantage of being easy to shut off, in contrast to the original which must be disabled or destroyed (if only due to their lack of understanding in how it operates). It comes with a removable power cell, allowing the user to break the connection at will. Alternatively, since the stones are placed on a flat panel and not attached in any way, they can simply by picked up to break the link.

Unlike the original, outside factors have been shown to disrupt the link to various degrees. Destiny's Faster-Than-Light engine creates a subspace disruption when engaged or disengaged, breaking the link for a few seconds. Heavy weapons fire directed at Destiny's shields will also break the link. Finally, the blue alien mind probe will sever the link if used on one of the two users, preceded by a bout of severe pain in the subject. When a blue alien that had handled a stone was killed moments before an attempted connection, Everett Young, who had connected to the alien twice before, was unable to connect to anyone, including Earth. The connection to Earth was eventually restored.

An additional side effect of the device not shown with the Alteran version is the transfer of traces of memory from the host body, which can be experienced in the form of brief visions or dreams. This version has also been shown to be able to connect to a completely alien species, namely the blue aliens, provided they have an active stone.

History
The Tau'ri had developed the variant of the communication device by 2009. At least one device was stationed at Icarus in anticipation of traveling through the Stargate to the nine-chevron address. When the base came under attack by an unknown force, an evacuation was immediately underway. However, rather than dial Earth, Dr. Nicholas Rush dialed the ninth-chevron address, effectively stranding roughly 80 Icarus personnel aboard the Ancient ship, Destiny. As the last person to evacuate the base, Col. Everett Young spent valuable seconds in securing a device. As a result, he was critically injured as the base exploded and he was flung through the Stargate and across the Gate room aboard Destiny. In the ensuing chaos, Rush discovered the device and discreetly made use of it. Afterwards, the device was used by the Expedition to keep contact with Earth and make visits to families. During Colonel Young's attempt to make a report to Earth, he switched bodies with a blue alien aboard a blue alien mothership. Later, Young used this to sneak aboard the mothership to try to rescue Chloe Armstrong. He ended up freeing Nicolas Rush instead, but using an alien mind probe broke the communications link and he was unable to restore it as Rush killed the alien who's body he'd been inhabiting.