The Sentinel is a planetary defense system on Latona which requires that its human Caretaker directly interface with it in order for it to be activated. The device removes invaders in flashes of light, presumably killing them.
Three hundred years ago, the Latonans built the Sentinel, a planetary defense system designed to protect the people while they pursued matters of the mind and spirit. This system had been successful in keeping the Goa'uld from invading these peaceful people's planet and taking them as slaves.
The Latonans were no longer aware of how their technology worked, they had technologically regressed and were fine as long as everything remained operational, but once something broke down, they were literally clueless.
A rouge NID unit came to Latona and took it apart just to reassemble it incorrectly. This left the planet subject to invasion by the Goa'uld Svarog. How ever Daniel Jackson of SG-1 reassembled it correctly. This reactivated the Sentinel and eliminated the Goa'uld
After these unfortunate events, it is most likely that the SGC was not permitted to return to Latona to learn of the Sentinel's technology. Any information that the SGC might have had access to died with Lts. Grieves and Kershaw.