Bats may sometimes enter a house through an open door or window, or a crack in the foundation, and decide to build a nest. If you suspect you have a bat in your house, the trick is to look and to listen.
Listen to your household noises, especially at night, if you think you have a bat. Common noises from bats are high-pitched chittering noises, fluttering noises (from wings hitting a wall or ceiling) and scratching.
Check your attic or basement first. Bats are drawn to dark, cool places, especially if there are high areas of moisture. Turn on all the lights to search for the bat. If you can't find it, but think it is in one of these places, wait for nightfall and leave the lights off, to see if the bat emerges.
Look everywhere in your house. Search every nook, corner or upper shelf in your home during the day to find where the bat is roosting. Typical signs of roosting include bat droppings, and possibly food scraps. Look underneath objects, such as plants, small towels and cushions. Bats are small and can hide easily when seeking darkness.
If you see a bat in one of your rooms, open your windows and doors to let it fly out. If you routinely leave open your windows and doors, this could have been how the bat got into your house in the first place. If you like to leave doors and windows open, add screens, so nothing can enter.