Outsourcing primarily takes away your personal span of responsibility around the activities you are outsourcing. You must consider all the security risks that you might have if you did all the activities in-house, but you have to rely on others to ensure that the work gets done. The number of guards used will depend on the location, crime index, and ebb and flow of the employees. Have standards, make the requirements a part of the contract, and put in an audit provision if you have any doubts.”]
Source: https://www.csoonline.com/article/2117216/outsourcing-physical-security.html