An inter-dimensional device, apparently of Ancient design, was discovered among the ruins of P9X-391 and brought back to Earth as a potential power source. Glyph symbols on the device are a form of the language of the Ancients and translate roughly as "Beings of the Inner Layer." The device is powered by crystals which glow when activated by touch, and it triggers an ability to see creatures that exist in a dimension parallel to ours. The device broadcasts a wave of energy particles which are apparently harmless and which attract these creatures to the device, and most sightings of inter-dimensional beings occur within a 500 meter radius. Touching the device imparts a kind of charge that can alter a body's electrical field enough to cause the inter-dimensional bleed-through effect, and the charge can be passed on from person to person by touch, resulting in the spread of the ability to see the creatures, which resemble enormous insects. Rearranging the configuration of the crystals causes the device to emit an opposite charge which can also be passed on through touch, and which essentially reverses the effect, making the inter-dimensional insects no longer visible.
Although the inter-dimensional device allows one to see creatures from another dimension, it does not actually shift an individual into an alternate dimension, unlike the Sodan cloak, also of Ancient design, which shifts an individual into another phase, but does not make inter-dimensional creatures visible. However, SGC modifications to the Sodan cloak did allow another kind of parasitic inter-dimensional creature to cross into our phase. There is no clear evidence that the two kinds of inter-dimensional creatures inhabit the same dimension.
Cross Reference: Alternate Dimension, Ancients, Crystals, Inter-Dimensional Insects, Inter-Dimensional Parasites, Invisibility, P9X-391, Vernon Sharpe
Episode Reference: Sight Unseen