Beacons were a system of near-instantaneous communication across the Protheans' galaxy-wide empire. They were made to interface with a person's brain, rather than through audio or video. Commander Shepard's 'vision', triggered by accidentally accessing a beacon, was actually a warning about the Reapers sent by the researchers on Ilos, in an attempt to reach any survivors and give them a message of hope. The message sent through them was coded specifically so that only Prothean minds could understand it. The Protheans hoped this would prevent any remaining Reapers from accidentally finding out that Ilos had survived. However, at that point, the Protheans did not fully understand the process of indoctrination, and they did not realise the message could be received and eventually understood b