In Luke 17:20-37 Jesus teaches the Son of Man would come unannounced like in the cases of Noah and the flood, and Sodom and Gomorrah.
Luke 17:20-35,37
[20]Some Pharisees asked Jesus when the Kingdom of God would come. His answer was, “The Kingdom of God does not come in such a way as to be seen.
[21]No one will say, ‘Look, here it is!’ or, ‘There it is!’; because the Kingdom of God is within you.”
[22]Then he said to the disciples, “The time will come when you will wish you could see one of the days of the Son of Man, but you will not see it.
[23]There will be those who will say to you, ‘Look, over there!’ or, ‘Look, over here!’ But don’t go out looking for it.
[24]As the lightning flashes across the sky and lights it up from one side to the other, so will the Son of Man be in his day.
[25]But first he must suffer much and be rejected by the people of this day.
[26]As it was in the time of Noah so shall it be in the days of the Son of Man.
[27]Everybody kept on eating and drinking, and men and women married, up to the very day Noah went into the boat and the flood came and killed them all.
[28]It will be as it was in the time of Lot. Everybody kept on eating and drinking, buying and selling, planting and building.
[29]On the day Lot left Sodom, fire and sulphur rained down from heaven and killed them all.
[30]That is how it will be on the day the Son of Man is revealed.
[31]“On that day someone who is on the roof of his house must not go down into the house to get any belongings; in the same way anyone who is out in the field must not go back to the house.
[32]Remember Lot’s wife!
[33]Whoever tries to save his own life will lose it; whoever loses his life will save it.
[34]On that night, I tell you, there will be two people sleeping in the same bed: one will be taken away, the other will be left behind.
[35]Two women will be grinding corn together: one will be taken away, the other will be left behind.”
[37]The disciples asked him, “Where, Lord?”Jesus answered, “Wherever there is a dead body, the vultures will gather.”