Failsafe mechanism

A Failsafe Mechanism or Fail-Secure is a device or mechanism which minimizes the damage to machinery and personel in the event of a failure in a system.

Atlantis sub-aquatic fail-safe
The Lantean scientist Janus progammed Atlantis to rise to the surface of the ocean should the Zero Point Module fall below a cirtain power level and be unable to hold the shield any longer. This program did not cause any on the city's systems to propel the city upwards, it simply released the clamps holding Atlantis to the bottom of Lantea's ocean, allowing it to float upwards without requiring any additional power from the ZPM.