The Language of Access Control
Lesson AC-1.1
Access control has its own vocabulary, and it overlaps with but is distinct from the BAS world.
Group: The Basics
Access Control System (ACS): The system that decides who can open which doors, when. At minimum: a credential, a reader, a controller, and locking hardware. ACS is used interchangeably with PACS (Physical Access Control System).
PACS: Physical Access Control System. The formal term in government and enterprise specs. Implies stricter credential and audit trail requirements.
Physical Security: The broader discipline: access control, video surveillance, intrusion detection, and perimeter security together.
AHJ: Authority Having Jurisdiction. The code official, inspector, or agency that decides whether your installation is compliant. In the field: Talk to the AHJ before you install magnetic locks on egress doors.
Group: Credentials and Identity
Credential: Anything used to prove identity. Cards, fobs, PINs, phones, fingerprints.
Proximity Card (125kHz): The original contactless card. No encryption, easily cloned. Still extremely common due to massive installed base.
Smart Card (13.56MHz): Encrypted, bidirectional communication. HID iCLASS, MIFARE, SEOS. DESFire EV2 and SEOS are the current security baseline.
Key Fob: Same technology as a card, different form factor. Clips to a keychain.
PIN / Keypad: A numeric code. Can be used alone or combined with a card for two-factor authentication.
Mobile Credential: Your phone is the card. Uses Bluetooth or NFC to communicate with the reader.
Biometric: Fingerprint, iris, palm, or face. Eliminates lost/shared credential problems but adds enrollment complexity and privacy concerns.
Facility Code: A site-wide number embedded in every card. With only 255 possible codes, the same codes get reused at thousands of sites.
Cardholder / Badge: The person record in the access management software.
Group: Reader Protocols
Wiegand Protocol: The dominant reader-to-controller interface for 40 years. Two wires, unencrypted, one-way. The data on the wire is completely unencrypted and can be intercepted.
OSDP: Open Supervised Device Protocol. The modern replacement for Wiegand. RS-485, encrypted, bidirectional, supervised. Always enable Secure Channel when available.
Clock and Data (F2F): An older reader interface. Still found on legacy hardware.
RS-485 (in access control context): The physical layer for OSDP and for controller-to-panel communication. Same wire standard as BACnet MS/TP.
Mullion Reader: A slim reader designed to mount on a door frame. Electrically identical to standard wall-mount readers.
Dual-Technology Reader: Accepts both 125kHz prox and 13.56MHz smart cards. Useful during credential migrations.
Group: Door Hardware
Electric Strike: Replaces the door frame's strike plate with one that releases electrically. Fail-secure (locked with no power) or fail-safe (unlocked with no power). In the field: Fail-secure vs fail-safe is a life-safety decision. Check with the AHJ.
Magnetic Lock (Maglock): An electromagnet that holds the door shut. 600 to 1,200 pounds holding force. Always fail-safe. In the field: Never install a maglock without a properly wired REX and fire alarm release.
Shear Lock: A concealed magnetic lock that resists shear force rather than pull force.
Door Position Switch (DPS): A magnetic contact switch that tells the controller whether the door is open or closed. Enables forced-door and propped-door alarms. In the field: Mount on the hinge side, not the latch side.
REX (Request to Exit): Any device on the secure side that allows free egress without a credential. Push buttons, PIR sensors, crash bars.
PIR (Passive Infrared): A motion sensor that detects body heat. The most common REX device on doors with maglocks.
Crash Bar / Panic Hardware: A horizontal push bar that releases the latch when pushed. Required by code on high-occupancy egress doors.
Electromagnetic Door Holder: Holds a fire door open until the fire alarm fires, then releases it to close automatically. Not an access control device.
Group: Controllers and Panels
Access Control Panel (ACP / ACU): The controller that receives credentials, evaluates access rules, and drives door hardware.
Mercury Security / HID Mercury: The dominant OEM controller hardware platform. Used by virtually every major access control software vendor.
Edge Device / Intelligent Controller: A controller built into or mounted directly at the door. Eliminates dedicated wiring to a panel room.
Sub-Panel / Reader Interface Module (RIM): Extends a main controller's door capacity over an RS-485 bus.
Head End / Access Management Software: Where administrators manage cardholders, access levels, schedules, and review event logs. Common platforms: Lenel OnGuard, Software House C-Cure 9000, Genetec Security Center.
Group: System Concepts
Access Level / Access Group: A named set of door/time-zone pairs assigned to a cardholder.
Time Zone / Schedule: A defined window of time during which an access level grants access.
Anti-Passback (APB): Prevents a credential from being used to enter a space it never exited from. Hard APB denies entry; soft APB logs the violation but grants access.
Tailgating / Piggybacking: An unauthorized person following an authorized person through a controlled door.
Forced Door Alarm: Triggered when a door opens without a preceding valid credential read or REX event.
Propped Door Alarm: Triggered when a door has been open longer than a configured time limit.
Shunt / Alarm Shunt: The controller temporarily suppressing door alarms during a window when a legitimate access event has occurred.
Two-Man Rule / Dual Authentication: Access requires two separate valid credentials from two different people.
Duress Code: A PIN that grants access but silently signals to the monitoring station that the person is under coercion.
Group: Integration
Video Badging / Camera Integration: Linking camera video to access events so operators can see who badged at a door.
VMS (Video Management System): The software platform that manages IP cameras. Common platforms: Genetec Security Center, Milestone XProtect, Avigilon.
Fire Alarm Integration: Doors on egress paths must release when the fire alarm activates. The release must be hardwired, not software-only.
Elevator Access Control: Using an access control system to restrict which floors an elevator can reach per credential.
BAS Integration: Connecting access control occupancy data to the BAS to adjust HVAC and lighting based on badging activity.
# PART 3: BLOG POSTS