[Rearden]

My parents house is incredibly old (in very good shape and restored but still old drafty attics and crawlspaces). When I was a youngin bats were a common thing. I can recall relaxing and watching Indiana Jones (the Raider's snake scene) in my room on the third floor when a bat came in and start flying around all disoriented like. After that of course my mom flipped out and had some professional come in and search the crawlspaces for where it came in and sealed it. The actual bat was dealt with by my father in the dining room with a fishing net.

My guess is the bat never left your house to begin with (or is coming in every night to get warm). As far as I know there arent many truly effective repellants. Try to find (or hire a pro to find) where it is gaining entry into your home (they can fit into INCREDIBLY small spaces.

Cats are useless in general and will not be able to stop a highly evolved creature of the night that uses senses far beyond what most other mammals have.

You need to stop the entry problem and then rely on a fishing net or broom (if you feel like murder) to solve the singular bat issue. Or you could call a pro (no idea what they charge)