Sometimes they come in through the fireplace if the vent/damper/flue is left open.
My friend woke up and went to use the basement potty one morning. No glasses on her peepers just yet. She saw something on the INSIDE of the toilet rim. Retrieved her specs.......you guessed it - BAT!! She ended up netting it with her 3 year olds butterfly net
We have had one or two in the cabin from time to time. They are freaky because they don't fly in a predictable pattern. We have done the stun them with a broom thing and sweep them out the door.
Good luck!