A Monocular is a compact, handheld telescope that magnifies the view of far-off objects for one eye instead of two like Binoculars.
History
Stargate Command personnel have used monoculars while off-world.
Colonel Jack O'Neill used one on P7S-441 while he kept a look out for the Jaffa pursuing Kaiael, who he and SG-1 for a time believed was member of their team called Lt. Tyler, due to a chemical the Reol secrete. (SG1: "The Fifth Man")
Lt. Colonel Cameron Mitchell used one on P9G-844 to watch the arrival of a Prior that they intended to capture. (SG1: "The Fourth Horseman, Part 2")
On M1B-129, Ronon Dex used a monocular while under the effects of a Wraith Mind manipulator. When he looked through the monocular, he saw a wraith instead of Lt. Colonel John Sheppard. (SGA: "Phantoms")