Cloak

A cloak is a device that allows an object to become invisible, either to the naked eye, sensors, or both.

Ancients
The Ancients employed cloaking devices in all of their puddle jumpers, which could be interfaced with the shield of Atlantis to cloak the entire city, a tactic that was used numerous time to hide the city from the Wraith. It is probable, therefore, that all Ancient vessels can be cloaked in a similar manner. Ancient cloaks render the ship invisible to the eye and all forms of sensors whilst using very little power. However, while a vessel is cloaked, they are vulnerable to attack as a shield cannot be raised. This is true for all races. It appears however that using Ancient cloaking technology, the ship still cannot be detected whilst passing through a planet's atmosphere, unlike the cloaks on Goa'uld Al'kesh which are detectable by heat.

The Ancients also invented the design later used in the cloaking devices of the Sodan.

Asgard
The Asgard use personal cloaking devices, which is applied to the body of an individual and then activated. These devices were used by an Asgard protected planet to hide from predators. The Asgard also employed a sophisticated form of cloaking technology in all Bilskirnir-class ships to mask their presence from all manner of scanning devices, including radar, and so the only way to detect them is with the naked eye.

Goa'uld
Goa'uld scout and cargo ships can be cloaked, and there has been one extreme case of Apophis cloaking an entire fleet of Ha'taks. Goa'uld cloaks can also be made small enough to be carried by individuals. Any Goa'uld ships passing through a planet's atmosphere whilst cloaked will give off a heat signiture that can be detected by other ships.

Nox
The Nox are apparently able to cloak both themselves and others naturally, which they have trouble maintaining while resurrecting someone. These cloaks evidently also have the property of making the target intangible as well as invisible (bullets, weapon]] blasts, and arrows will go through the spot where the target was last seen as if they weren't there). This is probably some sort of phase cloak, similar to Merlin's Phase device.

This form of cloaking is most likely achievable because the Nox are so near ascension.

Sodan
The Sodan use personal cloaking devices built according to Ancient instructions. These have the unusual property of allowing the user to see (but not otherwise interact with) out-of-phase matter, and can actually bring out-of-phase matter in-phase when deactivated.

Tau'ri
While the Tau'ri do not possessing conventional cloaking technology, the Odyssey acquired the ability to cloak thanks to Daniel Jackson when he used Ancient knowledge. At first, Carter had trouble getting the ship to decloak. However, they were eventually able to cloak and decloak the ship by simply pressing a few buttons. It is unknown if any of the other Daedalus-class ships possess this ability, though it seems likely, as Jackson probably just adjusted the shields, much like on puddle jumpers. He claimed that "having a ZPM helps" so its possible he utilized the ZPM on the ship in some manner while creating its cloak, or that it was not as efficient as those on other ships and required levels of power only a ZPM could provide.