Which device should be recommended for secure access to a central server room using a retinal scan?

The recommendation for a biometric scanner as the means for secure access to a central server room using a retinal scan is appropriate because biometric scanners are specifically designed to utilize unique physical characteristics for identification and access control. Retinal scans are a type of biometric authentication that analyze the unique patterns of blood vessels in the retina, providing a very high level of security due to the difficulty in forging such biometric data. This method is more secure than traditional password systems, as it relies on an individual's unique biological traits rather than something that can be forgotten, stolen, or easily replicated.

Other choices like a password keypad and a smart card reader involve methods that can be compromised by various means, such as shoulder surfing or even having the physical card stolen or duplicated. An access control panel typically serves as a management interface for these systems and does not provide the direct biometric authentication that specifically addresses the requirement of retinal scanning for secure access. Thus, the biometric scanner directly satisfies the need for secure, unique user verification through the identified method of retinal scanning.