Item from remembrance-of-earths-past by
A worldwide network of long-baseline gravitational-wave antennae — the trigger of the Dark Forest broadcast that would expose both Earth and Trisolaris to extermination — and the system Sophon's Droplets destroyed in a single coordinated strike at the end of Deterrence.
The system is the Swordholder's gun. As long as it exists and Luo Ji's hand is on the switch, Trisolaris cannot move against Earth without inviting a Dark Forest strike on both worlds. The moment Cheng Xin succeeds Luo Ji and proves she will not pull the trigger, Sophon's Droplets simultaneously destroy every antenna on Earth's surface in less than ten minutes. The Broadcast Era begins with their wreckage smoldering.
Several enormous cyclical-ring structures dispersed across continents and aboard the warship Gravity in deep space, each ring tens of kilometers across, suspended in vacuum chambers and tied into the deadman switch in the Deterrence Center. From orbit they glitter like rust-colored coins lying on the planet.