Badge readers are a core component of a Physical Access Control System (PACS). Their specific function is to authenticate an individual's identity via a credential (the badge) and then grant or deny entry to a restricted area. Crucially, every access attempt—whether successful or denied—is logged by the system, creating a detailed record of who accessed or attempted to access a specific location and at what time. This provides the precise function of detecting and recording access, which is essential for security audits and incident investigations.

A. Bollards are physical barriers that prevent vehicle access; they do not detect or record who is passing through.

B. Video surveillance records activity visually but does not inherently authenticate identity or create a structured access log like a badge system.

D. A fence is a static physical barrier designed to prevent or deter access, not to actively detect or log it.

1. National Institute of Standards and Technology (NIST). (2013, June). NIST Special Publication 800-116 Revision 1: A Recommendation for the Use of PIV Credentials in Physical Access Control Systems (PACS). Section 2.1, "PACS Overview," describes how a PACS "automates the passage of authorized people... while detecting and logging unauthorized entry attempts." The card reader is the key component for this interaction.

2. Massachusetts Institute of Technology (MIT). (n.d.). IS&T Knowledge Base - Card Readers. The documentation describes the function of card access systems: "MIT ID card readers are installed at the entrances to many buildings... to provide security and access control." These systems inherently log all card swipes for security purposes.