Zat'nik'tel

"This is a Goa'uld Zat'nik'tel. A weapon using a different form of energy, less powerful than that of a staff weapon. Less destructive, but still quite deadly."

- Teal'c

The Zat'nik'tel, nicknamed Zat or Zat gun by Colonel Jack O'Neill, is a handheld weapon used by the Goa'uld and their Jaffa. It is in the shape of a serpent and was first encountered by SG-1 on Apophis's Ha'tak. Its energy output, in the form of blue electrical energy, is less powerful than that of a Staff weapon. It's an extremely efficient weapon, used extensively by the Goa'uld, Tok'ra, Jaffa and the Tau'ri.

Overview
The Zat'nik'tel is a weapon of Goa'uld design. The safety is active when the Zat is not in use and lays flat like a snake, but when it is turned on it stands up, alert like a snake. The weapon is unique in how it affects objects, animate and inanimate. Zats have been in production for at least five thousand years. The technology itself may be similar to an Ori stun weapon.

Both the Zat'nik'tel and the Staff weapon resemble Goa'uld symbiotes.

Zat'nik'tel specifics
"The Goa'uld take great pleasure in discharging the weapon only once on a subject. Causing great pain, disabling them, but not killing them. The second shot will kill most subjects."

- Teal'c

Zat'nik'tels are fired by squeezing the bottom curve where the gun is held. The Zat is unique in the way it works. One shot is shown to incapacitate a victim and causes immense pain, while a second shot kills them. The shots do not have to be right after the other, as some have been killed several minutes after the first Zat blast; however, an extended period of time between shots will cause the effect to wear off and two new shots will be necessary to kill (as evidenced by Colonel Jack O'Neill's being shot a variety of times throughout SG-1's various exploits). A third shot will disintegrate the victim and their clothing, and will also disintegrate small inanimate objects with low densities, leaving no visible trace of their existence (this has been retconned out by the writers as they felt it was a bad idea. No other depictions of this 3rd shot has been seen since the 2nd Season.)

The Zat has been shown to conduct through objects, stunning victims indirectly. The weapon has also been used as a tool to boost hyperdrive speed when O'Neill used Ancient knowledge and required a short, powerful jolt to the modified engines, but is used as a tool to overload electronics in most cases as many conduits are not designed to handle that much energy in one blast. It is capable of disabling Aschen defense drones with one shot.

Zats have been shown to have little or no effect on Kull Warriors and Replicators, but they affect all other known species, including the Wraith.

It also appears that repeated attacks by this weapon causes most people to not suffer its effects with as much severity, as seen in cases where certain people are able to withstand the effects and remain conscious after a single shot. The second shot, on the other hand, is invariably fatal (on non-immune species) with only a single exception shown: When Major Samantha Carter's consciousness was replaced by an alien Entity, two shots left her body only brain-dead, allowing her consciousness to be transferred back into it.

Zat blasts can be caught and rendered harmless by a Kara kesh as shown by Cronus when he was fired upon by Teal'c. Also Setesh activated his shield on his Kara kesh which absorbed the blasts fired at him by SG1.

Trivia

 * The producers and nearly the entire crew of Stargate SG-1 believe that the third shot of a Zat is a bit of a deus ex machina, and some think that the third shot effect is a bit silly/stupid, often not wanting to refer to it outside when it is used. Others even think that it completely makes no sense, as stated in many of the Stargate SG-1 commentaries. The episode "Wormhole X-Treme!" even comments on the effect, with director of the show-within-a-show calling the disintegration idea "the stupidest thing..."
 * The "third shot" function of the Zat is only used three times in SG-1, and is mentioned one other time