The dimension observer is a device that was used by the Ancients. The device emits a field of particles that attracts interdimensional creatures. In this manner, the Ancients used the device to study these creatures.
Background Information[]
The device allows a person to see the creatures by altering the electrical field of the person by adding an extra charge; the charge is spread through touch. The device consists of several core crystals that can be rearranged in different ways to produce different effects, including producing the charge and anti-charge that allows one to see (or not see) the creatures.
History[]
SG-1 activated the device and brought it to Earth, but were eventually able to deactivate the device after a time. (SG1: "Sight Unseen")