Cooper joined Motorola, Inc., of Schaumburg, Illinois, in 1954, and earned his master's degree in electrical engineering from the Illinois Institute of Technology three years later in 1957. At Motorola, he was assigned to the division that was working on the first portable handheld police radios, which were introduced in Chicago in 1967. By then he had advanced to the position of operations director, and over the next nine years he made his most significant contribution to the future of mobile communications while serving the company.