G4S plc (formerly Group 4 Securicor) is a British multinational security services company headquartered in London, England.  The company was set up in 2004 when London-based company Securicor amalgamated with Danish business 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. 

G4S is the world's largest security company measured by revenues with over 10 billion U.S dollars in 2019. It has operations in more than 90 countries. With over 570,000 employees, it is the world's third-largest private employer, the largest European and African private employer, and among the largest on the London Stock Exchange.

G4S segments its business into two areas: 

Secure Solutions which includes services for commercial and government organisations in areas such as risk consulting, manned security, and security systems

Cash Solutions which is the outsourcing of cash cycle management for banks, financial institutions and retailers – making up 18 percent of G4S's turnover.

According to en.wikipedia