The Darchala's Chaos Device is an artifact found in both Heretic and Hexen. When used, it sends the player back to the start of the level (or near a portal the player came from in Hexen). It is best used to get out of unpleasant or dangerous situations (like, say, if the player is falling to his death; use of the artifact will instantly save him). The figure featured on the artifact closely resembles the "symbol of chaos" designed by Michael Moorcock.
In Heretic, if the player holds a Chaos Device when he is hit by the powered-up projectile of the Firemace (whose contact is normally lethal), the device will trigger automatically to save the player. However, the player will still lose half his health.