Zat'nik'tel, also known as a Zat gun, is a handheld weapon which emits a beam that stuns any living being, like a wireless tazer. It is a common sidearm among Goa'uld troops, kind of like a pistol is on Earth.
A zat is a small device partially resembling a snake. When inactive, it is folded up into a flat S shape, and when activated it will extend itself to resemble an alert snake. the weapon is fired by pressing
a small button on the side of it.
Zat fires a different type of energy than a staff weapon
. Unlike a staff, a zat fires a beam which will stun a person. The blast will cause the target great pain and impair movement, but the subject will sometimes stay conscious (the results wary based on the constitution and pain tolerance of the target). A second shot from a zat will kill the person. The second shot does not have to come straight after first, as people have been killed by a zat after receiving two shots with several minutes between. It is not known how long it takes for energy of zat to dissipate, and it likely also depends on the physiology and endurance of the target.
When they were first introduced, a third shot from a zat would disintegrate a target. This would be useful for getting rid of dead bodies and removing evidence, but was later retconned out of existence because the writers felt it was stupid. The idea of a third shot disintegration was even made fun of on the show.
Zat'nik'tel charge can be transmitted through carious metals, and has a deleterious effect on any electronic equipment. This indicates that the charge is possibly electro-magnetic in nature.
Zats are completely useless against Kull warriors and replicators, which can absorb energy directed against them, but are effective on any organic being. They are also more effective than a wraith stunner, because it only takes one shot to knock out a target.
Zats were created and used primarily by the Goa'uld, but in recent years the staff and security teams of SGC have also began to use zats as personal weapons. Other factions who rose after the defeat of the Goa'uld also employ them.