G4S is a British multinational private security company headquartered in London, England. The company was set up in July 2004 when London-based Securicor amalgamated with Danish firm Group 4 Falck. The company offers a range of services, including the supply of security personnel, monitoring equipment, response units and secure prisoner transportation. G4S also works with governments overseas to deliver security services.

Allied Universal is an American private security and staffing company, based in Conshohocken, Pennsylvania and Irvine, California. Formed in 2016 by the merger of AlliedBarton and Universal Services of America, Allied Universal is the world's largest provider of private security guards. It is also the third largest United States–based employer globally with 800,000 employees.