Thor's Hammer
From The Stargate Omnipedia
Asgard energy field of high intensity, preventing an Ettin (enemy of the gods, in this case the Goa'uld) from escaping a Cimmerian subterranean prison. Shaped in the general T-formation of Thor's fabled hammer, the device stands more than a dozen feet tall. The hammer, integrated into the doorway of the only exit of the caves, permits passage for Humans, but not Humans or Jaffa with Goa'uld symbiotes.
If in the energy field long enough, the Hammer will kill the symbiote and set the host free.
KEY EPISODE
Thor's Hammer - O'Neill and Teal'c are trapped in a cave beneath the surface of Cimmeria and are forced to fight an Unas to Thor's Hammer in the hopes of escape.