Which of the following is a common form of building access control?

• A. ID badges
• B. Passwords
• C. Retina scans
• D. None

Answer: (A)

For building access control, the most common form is ID badges. People wear badges that display a photo and a credential, and doors have readers (RFID, proximity, or barcode) that scan or detect the badge to determine if the wearer has permission to enter. This approach is widely used because it is inexpensive, scalable, and easy to issue and revoke—if someone leaves or changes roles, their badge can be deactivated quickly. It also provides an audit trail of who accessed which doors and when. Passwords are used for digital systems, not typically for physical doors, though keypad entry exists in some cases. Retina scans are more specialized biometric solutions that require costly hardware and maintenance, making them less common for everyday building entry. So ID badges are the best answer.