The Pinkerton National Detective Agency was a security guard agency established in the United States in 1850 by Allan Pinkerton. Businessmen hired Pinkerton guards to keep strikers and suspected unionists out of their factories, the most notorious example being the Homestead strike. The agency's logo, an eye embellished with the words "We Never Sleep" inspired the term "private eye."

Pinkerton is now a brand name for security guard services provided by Securitas.