Private security/armored companies are risk managing companies by definition. These companies are under constant external and internal threat due to the nature of their job.
It is imperative to these companies to train and control their human factor as much as possible. Most of losses and robberies happen with internal help or information. A lack of discipline in employee selection and monitoring could damage company's reputation and business.
This is why security companies use polygraph examinations to scrutinize and detect employees with criminal history and intentions at a selection stage with pre-employment polygraph and guarantee the honorability of their service with the investigation of any loss or complaint with specific case polygraph.
A specific case polygraph should make part of a standard procedure of a private security company to deter and detect possible internal flaws and confirm the superior quality of their services.