If you don't know where the bat is, you are truly in a difficult position because how do you prove that the bat is no longer in your house? I.e., how do you prove a negative? Here are some places you should check. Check with thick, preferably leather, gloves and a flashlight. NEVER put your hand somewhere before looking. Don't do any blind sweeps.

Check high first, behind curtains and wall hangings.

Check low, on the floor under items (bats can crawl). Generally bats can be anywhere, and they can fit in holes with diameters of 3/8 inch.

If the bat begins to fly, stay calm. Do not let the bat out of the house unless you are certain that no one has been exposed to the bat. Consult your state’s health department for the bat rabies protocols in your state. See the bat control link below for specific rabies protocols that some states have adopted.

Wait for the bat to tire and land. Wearing thick leather gloves, hold a large-mouth glass or plastic container. Then cover the bat with the container so that it is trapped inside. Take a stiff piece of paper and slide it between the wall/surface and the rim of the wide-mouth container, thereby trapping the bat inside. Secure the bat inside. If someone or something was exposed to the bat, then have the bat tested for rabies by your local health department or veterinarian. Otherwise, if no exposures took place, then the bat may be released. The proper release procedure is to place the trapped bat against a tree and then slide the paper out and then remove the container. Releasing the bat against the tree allows the bat to continue to rest while being safe from potential predators like the neighbor’s cat. This method also has the advantage of being harmless to the bat.

What if you never find the bat? The U.S. Centers for Disease Control and Prevention (CDC) states on its Web site that "People usually know when they have been bitten by a bat. However, because bats have small teeth which may leave marks that are not easily seen, there are situations in which you should seek medical advice even in the absence of an obvious bite wound. For example, if you awaken and find a bat in your room, see a bat in the room of an unattended child, or see a bat near a mentally impaired or intoxicated person, seek medical advice and have the bat tested." In addition, CDC emphasizes, "Remember, in situations in which a bat is physically present and you cannot reasonably rule out having been bitten, safely capture the bat for rabies testing and seek medical attention immediately." There are case histories of people with no apparent bites dying of rabies. If this bat is never found, and the bat was in a room with a sleeping person, in the room of an unattended child, or near a mentally impaired or intoxicated person, seek medical advice. More detailed information on this can be found at links listed below.

On Line Resources

CDC
Bat rabies
Bat Control