Sheh-fet was an elaborate surveillance network created by the Kinahhi people on the planet Kinahhi. It involved channeling the neural energies of the subjects- typically convicted criminals- to create a complex semi-telepathic network, able to detect even the potential for rebellious actions against the government. Its existence was justified by the presence of the Mar'bahl, a race who had previously lived on this planet and were believed to have ties to Ba'al, who the Kinahhi had once served.
Senator Robert Kinsey was able to set up his own sheh-fet on Level 17 of the SGC after forming an alliance with the Kinahhi while SG-1 were away for four months rescuing SG-10; due to the time dilation effect, what took SG-1 only a few hours took four months outside the effects of the gravitational pull. After this system was discovered by General George S. Hammond and his replacement at the SGC, both men exposed its existence and got it shut down by the President.
The system on Kinahhi was shut down for good when Daniel Jackson linked himself to it, having determined that the 'Mar-bahl' actually had ties to the Ancients, using his unique knowledge of them from his past Ascension to convince the Kinahhi that their alleged enemies meant them no harm. Colonel Jack O'Neill was able to use his superior Ancient gene to destroy the device for good and free those trapped by it. The city of Tsapan where the device was located was subsequently destroyed during a battle with the Kinahhi military. (SG1: "A Matter of Honor", "The Cost of Honor")