I'm not sure of what a "typical louvered door" is... but would a deadbolt keyed on both sides work? In other words, you need a key to get out of the locked door as well as in.

You just have to be SURE that the key is not in reach of the door from the outside, but that you can ALWAYS find it if there's an emergency like a fire. I have window in my front door. When I'm home, the key lives in the inside lock, but if I'm gone it hangs and a hook near the baseboard right next to the door.