What are the dangers of having the front door open?

I live in a rural area on a small island with no crime, in a large house. There is a door on the ground level which I didn't close properly so it was open about 0.5 cm (quarter of an inch) between 10 pm and midnight. When I had seen it, I isolated the entire floor, but I didn't want to wake up my family. What should I do? How do I know if something got in? Am I in danger from something, because my room is a meter away from that door?