The Coppelius beacon was a type of homing beacon that could create a rift in the space-time continuum, allowing synthetic beings from another galaxy or dimension to enter local space. Information on constructing this technology was hidden in the Admonition. (PIC: "Et in Arcadia Ego, Part 1")
In 2399, this beacon was constructed by synthetics on the planet Coppelius. This technology allowed the tentacled artificial lifeforms to (briefly) cross over into local space through what appeared to be a wormhole or interdimensional rift before Soji Asha shut down the beacon and forced the portal to close. (PIC: "Et in Arcadia Ego, Part 2")