Both the sales office and the security company can be employers, depending on the employee's employment relationship and labor contract. The employing unit refers to an organization or individual that enjoys the management right in labor relations and pays wages to workers. Whether it is a sales office or a security company, it can be regarded as an employer if it hires employees and establishes a labor contract relationship with them.

Sales offices are generally sales departments set up by real estate developers, which are responsible for selling real estate houses and services. The sales office can employ salespeople, account managers, administrative personnel, etc. They have established a labor contract relationship with the sales office, which is their employer.

Security companies are enterprises specializing in security services, providing security services such as security, patrol and access control for customers (such as communities, enterprises and institutions, commercial places, etc.). The security company employs security guards and signs labor contracts with them. In this case, the security company is the employer of the security personnel.

It should be noted that the employers of temporary workers such as construction workers and cleaning staff who are temporarily employed by sales offices or security companies may be temporary labor service companies. Therefore, the specific situation needs to be determined according to the employment contract and labor relations.