The weapons disabler is Tollan technology used for security purposes. A blue beam of light scans visitors and detects and disables any form of weaponry which passes through it. Only the weapons of the Tollan security forces remain unaffected. O'Neill stole one of the devices from the Tollans as part of the ruse to expose and apprehend the rogue NID teams who were stealing alien technology.
Cross Reference: Tollans
Episode Reference: Pretense, Shades of Grey, Between Two Fires