The sentinel hypothesis is the suggestion that if advanced alien civilizations exist they might place intelligent monitoring devices on or near the worlds of other evolving species to track their progress. With the increase of Near-Earth Objects being reported, there is a compelling argument that “lurkers” or “sentinels” may be directly observing us instead of ETs. Clyde will give possible examples of what these sentinels are like and how they are used to monitor us. These probes may have been sent by multiple civilizations; many or most of whom could well be currently extinct. However, for the civilizations that may be spying on us – the greatest galactic currency is knowledge.