The probability of alien life existing is unknown. That also entails the probability of alien life existing that is observing us is also unknown, and there are reasons to think we might be under observation. For hundreds of millions of years now, any alien life within, say, a thousand light years with a decent sized telescope would have determined we're an interesting planet that warrants further study: we orbit a stable main-sequence star with a nice percentage of heavy elements, we're in the "goldilocks zone" for liquid water, and our atmosphere has tell-tale biosignatures. So, anyone think they're watching us? Or maybe already here?