Panic button
From Halopedia, the Halo wiki
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 had failed and they needed immediate assistance. The green signal merely activated a homing beacon to inform UNSC forces of the location of a hidden objective.
In 2525, the Spartans used a panic button to mark a homing beacon on Eridanus Secundus. Despite this, the asteroid base survived until 2552.
