This race, just like the Covenant, is not actually a single race. The original base race were synthetic machines adapted to the ever changing universe. Over the decades and after assimilating various races to form their own army, they have become a highly fearsome race.
Mass Effect 3 showed us the full extent of their assimilation by forcing the Humans, Turians, and Asari races to fight while imbuing them with their sentient technology. Living ships size creatures were also seen and attacked the whole of every race in the galaxy. Their Goal?
The assimilation of the new races and abilities then go back into hiding. They leave the last race standing to regrow and let the universe begin again. They wish only to repeat this cycle and serve as monitor and decider.
You cannot avoid the gaze of the Reapers, in fact they have most likely already seen us. All we can do is prepare for a huge fight and band together with other races in order to put a stop to this vicious cycle. However since we have yet to reach past our own Solar System, I'm fairly certain we're safe.