Earthquake Early Warning Systems (EEWs) provide seconds to tens of seconds of lead time by exploiting the faster propagation of P waves relative to the more damaging S waves. We study and test the performance of two EEW systems, the Earthquake Alarm Systems (ElarmS) and the Virtual Seismologist (VS). ElarmS is developed by the University of California, Berkeley, and is part of the U.S. west-coast-wide ShakeAlert EEW. It rapidly associates P-wave triggers across stations and uses early amplitude metrics (e.g., peak displacement) with empirical ground motion scaling relationships to estimate origin time, epicenter, and magnitude. VS is currently maintained by the Swiss Seismological Service at ETH Zurich and is using a Bayesian approach using observed picks and the earliest available ground motion amplitudes, based on predefined prior information and envelope attenuation relationships, in order to estimate earthquake magnitude, location, and the distribution of peak ground shaking. We have tuned, configured, and operated these two systems for the broader Greek region, also focusing on the Attica region and the Corinth Gulf, benchmarking alert latency, epicentral misfit, and magnitude residuals against the National Observatory of Athens (NOA) revised bulletin. Results include regional latency maps and accuracy statistics that elucidate speed–accuracy trade-offs and network geometry effects for operational EEW in Greece.