 Stewart also self-published several books, doing business as Santa Rita Technology, and later as Covox, including "The Analog Ear Story" and "The Analog Ear–brain System" in 1964, and "The Bionic Ear" in 1979.The research resulting from analog ear studies fueled the creation of special sounds for use in repelling birds and other pests.Sounds were synthesized to follow natural bird calls but were of a switching kind.