The sonic weapon is technology of the people of Talthus. It emits a high pitched humming tone and appears as a glowing ball of light that travels quickly and engulfs the victim, rendering him unconscious but causing no permanent damage.
When the spaceship, the Stromos, crashed on P2A-347 carrying the last survivors of Talthus in stasis, several of the stasis compartments began to fail. SG-1 discovered the ship, and Pharrin, desperate to save the last of his people, remained in hiding and used a hand device to release the sonic weapon and cause the team to pass out. He then used the opportunity to download at least a dozen personalities into Daniel before the team began to regain consciousness.
Cross Reference: Pharrin, Stromos, Talthus
Episode Reference: Lifeboat