Mass Effect & Mass Effect 2
The beacon was a Prothean artifact unearthed on the Alliance colony of Eden Prime. Its resemblance to the Prothean data banks recovered on Mars provoked immediate interest from the Alliance and Citadel Council. It proved to be a solid state data storage device, part of a galaxy-spamming comm network similar to the modern extranet. Intact Prothean 'paleo-technology' is rare; the beacon seemed to promise another quantum leap of technology, akin to the discovery of the mass effect drive and relays.
Unfortunately, the beacon also drew the attention of the rogue Spectre Saren Arterius and his synthetic allies, the geth. A dawn raid by his flagship Sovereign resulted in hundreds of civilian casualties. The beacon was badly damaged. The motives behind the attack are still being investigated.
During the recovery operation, the beacon fired a pulse of energy at the Executive Officer of the Alliance frigate Normandy. Lieutenant Commander Shepherd survived and appears to have suffered no ill effects. Afterwards, the beacon fell inert. The mechanism appears to be dead.