A panic button is a single-shot emergency beacon employed by the UNSC Armed Forces. It has two settings: The 'Red' setting sent out a distress signal, informing allies that the team's mission has failed and they need immediate assistance. The 'Green' signal merely activates a homing beacon to inform UNSC forces of the location of a hidden objective.
In 2525, SPARTAN-II Blue Team used a panic button to mark a homing beacon on Eridanus Secundus. Despite this, the Unified Earth Government was soon embroiled in the Human-Covenant War, and so the asteroid base survived until 2552. This particular beacon had exceptional longevity, as its signal could still be picked up by the UNSC Gettysburg twenty-seven years later.