Homing beacon
A homing beacon was a communications device that sent a signal, to help find someone or something. 

In late-2364, the parasitic beings that attempted to take over Starfleet Command by inhabiting high-ranking officers, activated a homing beacon so their homeworld could locate Earth and attack again in the future. ()

In 2399, synthetics on the planet Coppelius constructed a beacon capable of transmitting a signal to a higher race of synthetics based on information acquired from the Admonition. 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. ()
Communications technology