Repel the Bats by Bad Smell
Repel by Odor
Naphthalene (crystals or flakes) is the only chemical currently registered as a bat repellent for indoor use. Naphthalene should be applied at the rate of five pounds per 2,000 cubic feet of attic or wall void space. As the material vaporizes, the bats will be repelled and will not return so long as the strong odor remains. Once the material dissipates, the bats will return. Humans should avoid breathing the fumes and sensitive people or those with respiratory problems should avoid all treated areas.
Dr. T's Nature Products - Bat-A-Way is made from 100% naphthalene and is used inside buildings. Eight ounces are spread on floors or between walls for each 200 cubic feet of inside space. It also comes as a fogger.
Repel the Bats with Sound
Sound - Bats may be repelled by high-frequency sound devices, although this is the least effective method and not highly recommended. An inexpensive device can be made by attaching a silent dog whistle to an aquarium pump. Place the device in the roosting area and run continually until the bats leave. Since sound does not penetrate solid objects, many sound devices may be required.
Repel the Bats With Light
Light - Bats may be repelled by brightly illuminating their roosting area, although bright lights can be a fire hazard, are inconvenient and expensive. The attic of an average size house may require four or more 100 watt bulbs to drive out the bats. Illuminate all potential roosting sites and check the roost after several days. The addition of windows in an attic may help reduce the likelihood of bat roosts.
Repel the Bats With Touch
Air Drafts - Strong breezes and cooler temperatures created by open windows or fans can repel bats. Drafts from carefully directed electric fans have successfully repelled bats.
Sticky Substances - Sticky substances used to prevent birds from roosting is also effective for bats. The substance does not trap the bat, but makes it unpleasant for the bat to stay. The Tanglefoot Company sells a sticky material that can be used in this manner.