Building access control is the system of credentials, readers, and doors that decides who can enter a facility, and by design it can only confirm that a valid credential was presented at a door, not who is actually walking through it.
That distinction matters more than most facility teams realize until an incident forces the question. An access control system logs a badge number, a door, and a timestamp. It does not log a face, a headcount, or how long a door stayed open after that log entry closed.
- Most badge readers still use the 125 kHz proximity format or the 13.56 MHz smart card format defined in ISO/IEC 14443.
- Reader-to-controller wiring runs on the older Wiegand interface, typically in a 26-bit format, or the newer OSDP protocol, which supports AES-128 encryption.
- PoE cameras and readers draw up to 15.4 watts under the 802.3af standard or up to 30 watts under 802.3at.
- There are 4 blind spots every credential-based access control system shares: tailgating, doors held open, forced doors, and badge-person mismatch.
- Fire and life-safety codes such as NFPA 101 require doors on an egress path to allow free exit without a credential.
What Building Access Control Actually Verifies
Building access control verifies one fact: that a credential presented at a reader matched an entry on an authorized list. Everything the system reports afterward, a door opened, a badge number, a timestamp, is built on that single verification, and the system has no independent way to confirm anything beyond it.
Credentials and Readers
A credential can be a proximity card, a smart card, a mobile phone, or a PIN, read by a device wired to a door controller. Most readers still speak Wiegand or the newer OSDP protocol to the controller, and most cards in the field use 125 kHz proximity technology or the 13.56 MHz smart card format defined in ISO/IEC 14443. None of this hardware asks whether the person holding the card is the person it was issued to. See our guide to key card entry systems for how the credential type itself affects how easily a badge can be cloned or shared.
The Audit Trail
Every valid and denied attempt gets written to a log, and that log is genuinely useful for compliance and after the fact review. It is also, by construction, a record of credential events rather than a record of people. A log with a clean, uninterrupted string of valid entries can still describe a door that let in more people than badges scanned. Where that log can be tied to a specific individual, it is also personal data under regulations such as GDPR, and Article 15 gives that person a right to request the data an organization holds about them, which most facility teams handle as a records request rather than a security question.
The Four Blind Spots in Every Access Control System
Four situations sit outside what a credential based system can see on its own, and each one tends to show up in an incident report after the fact rather than at the moment it happened. These four gaps show up daily across commercial venues such as office towers, retail centers, and mixed-use campuses, where dozens of doors and a constant flow of visitors make manual monitoring impractical.
- Tailgating: a second person follows a valid badge through the door before it closes.
- Door held or propped open: the door stops requiring a credential for as long as it stays open.
- Forced door: the door opens without the reader, so no credential event gets created.
- Badge and person mismatch: a valid badge is used by someone other than the person it was issued to.
| Event | What the Access Log Confirms | What It Cannot Confirm |
|---|---|---|
| Door opened with a valid badge | A registered credential matched an entry on the authorized list | How many people actually walked through |
| Door left open past its cycle time | The last valid scan recorded at that door | That the door stayed open, propped or unattended, afterward |
| Door opened without a reader | Nothing, unless a separate door position sensor is wired in | Who opened it or how |
| Badge used at a reader | The badge number on file for that credential | Whether the holder is the person the badge was issued to |
Tailgating and Piggybacking
A valid badge opens the door, and a second person walks through behind the first before it closes. The reader logged one credential and one entry. The door itself let two people through, and the access control system has no way to know that happened.
Doors Held or Propped Open
A door held open past its normal cycle time, propped with a wedge or a chair, stops requiring a credential at all for as long as it stays open. The access log shows the last valid scan and nothing about the open door standing unattended afterward. On doors that sit along a fire egress path, codes such as NFPA 101 also require the door to allow free exit without a credential at all, which limits how a facility can lock down a propped door without creating a life-safety conflict.
Forced Doors
A door forced open without using the reader generates no credential event whatsoever. Depending on the hardware, a door position sensor might raise a separate forced entry alarm, but the access control log itself stays empty for the exact moment that matters most. Exterior readers exposed to forced-entry attempts are often rated IK10 under the IEC 62262 vandal-resistance scale, meaning the housing is built to withstand a 20-joule impact without losing function, though the rating covers the reader enclosure, not the door itself.
Badge and Person Mismatch
A lost, shared, or stolen badge opens the door exactly as well as one still carried by its original holder. The system verifies the card, not the face behind it, so a badge issued to one employee can be used by someone else indefinitely without a single denied entry appearing anywhere in the log.
Why Access Control Alone Cannot Close These Gaps
Access control was built to answer a credential question, not a visual one, and no amount of tuning the reader or the controller changes what the hardware is capable of observing. A door controller receives a signal from a reader and a signal from a door position sensor. It has no camera, no headcount, and no way to compare the badge on file to the person standing at the door. Federal guidance from the National Institute of Standards and Technology treats physical access control as one layer of a facility’s security posture, not a complete visual record of it. Homeland security and critical infrastructure operators face an added requirement: any camera added to close these gaps on a federally funded site must comply with NDAA Section 889, which restricts certain video surveillance equipment from federal networks and federally funded projects. Closing the four gaps above requires a second data source that actually sees the door, not a better version of the same credential check.
Why Video Is the Standard Answer
Adding video to an access controlled door is the standard way facility teams close the visibility gap, because a camera captures exactly what the badge reader cannot: how many people passed, whether the door stayed open, and whether the face at the door matches the badge on file. The Cybersecurity and Infrastructure Security Agency lists physical access control as one layer of facility security for critical infrastructure operators, not a complete one on its own.
What Integration Requires in Practice
Pairing video with access control in practice means the camera has to be tied to the same event, at the same door, at the same moment as the badge read, or the two records are just two separate systems that happen to share a building. A camera on a shared network switch, powered over Ethernet under the 802.3af standard at up to 15.4 watts or the 802.3at standard at up to 30 watts, and exposed through an ONVIF Profile S or Profile T compliant stream, is usually straightforward for an integrator to add at a door that already has a reader and a controller. That network cabling is also subject to the same 100-meter limit the TIA/EIA-568 standard sets for a Cat6 run before a switch or repeater is required. The harder part has traditionally been the software: correlating a badge event in the access control platform with the right few seconds of footage from the right camera, without a person doing that matching by hand after an incident.
Frequently Asked Questions
What is building access control?
Building access control is the system of credentials, readers, controllers, and software that determines who can open which door in a facility and when. It confirms that a valid credential was presented at a reader, and logs that event with a timestamp.
Can building access control detect tailgating on its own?
No. A credential based system logs one badge scan per event and has no way to know whether a second person followed through the same open door. Detecting tailgating requires a camera at the door, not a change to the reader or controller.
Does an access control log show whether a door was propped open?
The log shows the last valid credential scan at that door. It does not show how long the door stayed open afterward, so a door propped open after a valid scan leaves no separate record in the access control system.
How do facilities usually add visibility that access control alone does not provide?
Most facilities add cameras at doors that already have readers and controllers, then correlate the camera feed with the badge events already being logged, rather than replacing the access control system itself.
Does adding video to access control mean replacing the readers or turnstiles?
No. Video is added on top of the credentials, readers, and controllers a facility already has installed. It closes the visibility gap at the door without changing the hardware that grants entry.
Does NDAA Section 889 affect cameras added to an access-controlled door?
It can. Facilities operating on federal networks or federally funded projects, including many in the homeland security and critical infrastructure space, need any camera added at a door to comply with NDAA Section 889’s restrictions on certain video surveillance equipment before it is installed alongside the existing readers and controllers.
Argu runs on the cameras already mounted at doors that already have readers and controllers, and it turns each blind spot above into a rule stated in plain language, for example a door on the third floor held open for more than thirty seconds after eight in the evening. It does not replace the reader or the turnstile. It watches the door those systems cannot see past, using facial recognition for the badge and person mismatch case and people counting for tailgating. To see how a rule like this gets set up on the doors a facility already has, talk to Argu about closing access control blind spots.
Last updated: September 2026
