Not involved in this, I'm guessing this is how it goes: there are algorithms that automatically register the image that was just taken, diff it with a reference image of the sky from before, and if there's a significant difference that passes some false positive tests, then there's some notification for human intervention.
Indeed there could be events we are missing right now. Astronomers are building instruments that have larger fields of view (e.g., LSST), so that they can scan the sky ever few days.
Indeed there could be events we are missing right now. Astronomers are building instruments that have larger fields of view (e.g., LSST), so that they can scan the sky ever few days.