The Sentinel is a planetary defensive weapon, built over 300 years ago by the inhabitants of Latona. It has kept them safe from the Goa'uld for generations, although the current population no longer knows how the device functions. The Sentinel is protected by a force field using a constantly changing code based on a mathematical progression of harmonic tones, and it is monitored by a human Caretaker. Symbols written on the device, similar to those on P2A-463, translate as "Life Energy" and "Two as One," indicating that the Caretaker must join with the Sentinel, and together the life energy of man and machine will activate a powerful weapon that dematerializes enemy forces. When rogue NID operatives tried to steal the Sentinel technology and killed the Caretaker, Latona was left defenseless. On the return SG mission to Latona, the invading Goa'uld were destroyed when Colonel Grieves activated the Sentinel by joining with it in the Caretaker's place.
Cross Reference: Caretaker, Sean Grieves, Lieutenant Grogan, Lieutenant Kershaw, Latona, Marul, NID Off-World Operation, NID Rogue Operation, Svarog
Episode Reference: The Sentinel