Swintec thrived on this type of government business, but sales were declining by the late 1990s. Then the company stumbled on an idea: a clear typewriter for prisons. The company's owner, Dominic Vespia, says they were inspired by other transparent products designed to prevent smuggling of contraband, from televisions to toothpaste tubes.

Though Swintec is profitable, it has slimmed down to about 10 employees from about 85 employees, Mr. Michael says. He says the company sold "thousands and thousands" of typewriters at the peak but declined to be specific. Swintec still sells about 3,000 to 5,000 typewriters a year, to customers including universities, senior centers and state and federal prisons.

Swintec is one of the last surviving typewriter companies in the U.S., although these days its machines are made in Japan and Indonesia.

Swintec started out in 1978 selling electronic calculators. By the mid-1980s, its typewriter sales were growing fast, even as the personal computer was cutting into sales at typewriter giants.

And Swintec executives found a way to save their business a decade ago with a new client: prisons.