Which of the following will allow a company to implement the MOST cost-efficient way to easily identify whether a user has secure access to particular areas of a building?

Access badges - particularly smart card or proximity card badges - are low-cost per unit, easy to issue and revoke, and can be integrated with electronic door readers to log entry events for auditing. They provide a balance of cost efficiency and security that scales easily across an organization without requiring specialized hardware at every access point. This makes badges the most practical and widely adopted solution for identifying and controlling access to secured building areas.

Retina scanners are expensive biometric devices with high per-unit hardware costs, specialized installation requirements, and ongoing maintenance overhead, making them cost-prohibitive for most organizations.

Firewalls are network security devices that control data traffic between networks and have no function in identifying or authorizing a person's physical access to a building.

Key fobs, particularly hardware TOTP tokens, have a higher per-unit cost than proximity badges and must be replaced periodically, making them less cost-efficient than standard badge systems for physical building access.