Who knows how he got in there, but the chimney seems likely. They don't need but a very small crack, by the way.

I would VERY much leave the door open! Turn off the lights in the basement, and open the door until you go to bed.

I had 2 bats get into this house when I was renovating it last year. When I discovered them, it was daylight and the first one was hanging onto the lath upstairs. Second one was hanging onto the plaster wall downstairs. Very easy to just gently get a hold of them and take them outside. Neither tried to fly. I know how mine came in and it was fixed.

I would see if it's not just hanging on downstairs during the daylight. If not, do what rhizo says.

Leave the windows and doors open, so it can escape, if it is still alive.

Well, DH evicted the bat yesterday PM. Found him asleep or injured on the floor in front of the door. Guess I'll have to go up on the roof one of these days and see what's what. Seems weird that he would have climbed all the way from the roof to the basement thru the chimney, tho. That's a long way to go.

Thanks for the suggestions.

I would suggest that everyone be very careful with bat encounters. Bats are frequently carriers of rabies, which is 100% fatal after symptoms appear. Often times bat bites are unnoticable as well. I don't want to scare anyone, but I would consider contacting my local health department and getting their advice if you woke up with a bat in your room or you had close contact with a bat, especially if it was acting strange. It is also easier for testing if the bat is captured so it can be tested for rabies. Just my 2-cents

TBT