The Devil Bat (1940)

Dr. Carruthers feels bitter at being betrayed by his employers, Heath and Morton, when they became rich as a result of a product he devised. He gains revenge by electrically enlarging bats and sending them out to kill his employers' family members by instilling in the bats a hatred for a particular perfume he has discovered, which he gets his victims to apply before going outside. Johnny Layton, a reporter, finally figures out that Carruthers is the killer; after putting the perfume on himself, he douses it on Carruthers, hoping it will compel him to give himself away. One of the two is attacked as the giant bat makes one of its screaming, swooping power dives.