RFID & access control glossary

80 terms you'll meet when specifying readers, credentials, tags and door hardware — defined in plain English.

#

1:N face matching (One-to-many identification, Face identification)
Identification mode in which a face terminal compares a live capture against all N enrolled templates to find out who the person is, with no card or PIN. It is convenient, but matching time and the chance of a false match grow with the size of the database. 1:1 verification instead compares the face with one template selected by a card or ID, which is faster and more reliable for large user populations. See face recognition terminals.
86-box (wall box) (86-type back box, 86 mm wall box)
A square flush wall box sized for 86 × 86 mm faceplates with 60 mm fixing-screw spacing, widely used in Asia. Many readers, keypads and exit buttons are designed to mount on it. Its 60 mm spacing matches common European round flush boxes and is close to UK single-gang boxes (60.3 mm), but not the US single-gang box (83.3 mm / 3.28 in), so confirm the mounting pattern before ordering. See exit buttons.
8H10D format (10-digit decimal card number)
A common card-number format that takes 8 hexadecimal digits (a 32-bit card ID or UID) and shows them as a 10-digit, zero-padded decimal number; for example, hex 00BC614E becomes 0012345678. Many USB readers use it, and it is often the number printed on 125 kHz cards. Mismatched formats, such as 8H10D versus a facility code plus card number split, or reversed byte order, are a frequent reason cards do not match. See USB reader output formats.

A

Access controller (Door controller, Access control panel)
The panel that makes access decisions. It receives credential data from readers over Wiegand, OSDP or RS485, checks it against stored users, schedules and rules, then drives lock relays and monitors door status and REX inputs. Networked controllers connect over TCP/IP to management software and typically keep working from a local database and event buffer if the network drops. Common versions control 1, 2 or 4 doors. See networked door controllers.
AES-128 (Advanced Encryption Standard)
The Advanced Encryption Standard (FIPS 197) block cipher with a 128-bit key and 128-bit blocks. In RFID and access control it secures DESFire EV2/EV3 and NTAG424 DNA credentials, OSDP Secure Channel links and many encrypted readers, usually in mutual-authentication schemes with CMAC message integrity. No practical attack on full AES-128 is known, so real-world security depends on key management: unique keys, kept out of reach. See key diversification.
Antenna gain (dBi) (dBic)
How strongly an antenna concentrates radiated power in a direction compared with an isotropic reference, expressed in dBi; dBic specifies a circularly polarized reference. Higher gain can concentrate coverage without increasing total transmitted power. For a simple antenna budget, EIRP (dBm) equals conducted output (dBm) minus cable loss (dB) plus antenna gain (dBi). Check conducted-output limits, antenna-gain conditions, regional ERP or EIRP limits and the approved equipment configuration separately; a 4 W EIRP calculation alone does not establish FCC compliance. See circular vs linear antennas and UHF frequency by country.
Anti-collision (Singulation, Multi-tag reading)
The protocol a reader uses to separate and read multiple tags that are in its field at the same time. ISO/IEC 14443 Type A uses a bit-by-bit UID tree search, while Type B, ISO/IEC 15693 and EPC Gen2 use slot-based methods, with Gen2 adjusting the slot count through its Q algorithm. Anti-collision lets UHF readers inventory many tags at once, while access-control readers normally act on one card at a time. See EPC Gen2.
Anti-passback (APB)
A controller rule that stops a credential from being used twice in the same direction without a matching opposite event (for example, entering twice without exiting), so one card cannot be passed back to admit a second person. It needs readers on both the entry and exit sides. Hard anti-passback denies the violation; soft anti-passback grants entry but logs an alarm; timed anti-passback blocks reuse for a set period. See turnstile readers.
Armature plate (Armature, Maglock strike plate)
The steel plate mounted on the door that a magnetic lock's electromagnet attracts to hold the door closed. It is fixed with a central bolt and rubber washers so it can pivot slightly and seat flat against the magnet; mounting it rigidly reduces holding force. Lock-status versions sense whether the plate is fully seated. Brackets adapt the plate and magnet to different door and frame types. See maglock bracket guide.
ATEX / IECEx (ATEX Directive 2014/34/EU, IECEx scheme)
Distinct frameworks for explosive atmospheres. EU ATEX Directive 2014/34/EU covers equipment and protective systems; workplace Directive 1999/92/EC addresses worker protection and area classification. ATEX conformity routes depend on category and equipment type: category 3 can use internal production control, so a third-party certificate is not required for every category. IECEx is an international certification scheme based on Ex standards; confirm acceptance under the destination's rules. Review the declaration, instructions and evidence for the applicable route, and verify the current online IECEx Certificate of Conformity when claimed. Neither framework's name alone approves a particular installation. See hazardous-area access control.

C

Circular polarization (Circularly polarized antenna, CP antenna)
An antenna polarization in which the radiated electric field rotates as the wave travels, so a tag can be read at any rotation in the plane facing the antenna. Circularly polarized UHF antennas suit tags with unpredictable orientation, such as mixed cartons, at a cost of about 3 dB compared with a correctly aligned linear antenna. Linear polarization reaches farther when tag orientation is fixed. See circular vs linear antennas and UHF antennas.
CPU card (Microprocessor card, COS smart card)
A smart card whose chip contains a microprocessor and a card operating system (COS) rather than fixed memory logic. It processes ISO/IEC 7816-4 APDU commands, contactlessly via ISO/IEC 14443-4, and can host multiple applications with separate keys, typically using 3DES or AES. Mutual authentication and encrypted data make it far harder to clone than memory cards such as MIFARE Classic. In product listings the term usually means a 13.56 MHz contactless COS card. See encrypted readers.

D

Dense reader mode (DRM, Dense interrogator mode)
An EPC Gen2 operating mode for sites where many UHF readers work close together, such as adjacent dock doors or portals. Tags reply with Miller-subcarrier encoding, which places their responses in sidebands away from the reader transmit channels, and readers follow a tighter spectral mask. This reduces reader-to-reader interference. It usually lowers raw read speed but improves reliability in crowded installations. See warehouse RFID and fixed UHF readers.
Door status sensor (Door position switch (DPS), Door contact)
A switch, typically a magnetic reed contact, that tells the controller whether the door is open or closed. With it, the controller can raise door-forced-open and door-held-open alarms, relock as soon as the door closes, and run interlock logic. It connects to a controller input, commonly wired so the circuit is closed while the door is shut. See magnetic lock wiring diagrams and Wiegand reader wiring.
Dual-frequency reader (Dual-band reader, 125 kHz + 13.56 MHz reader)
A reader that combines 125 kHz LF and 13.56 MHz HF reading circuits, so one device accepts, for example, EM4100 cards and MIFARE or NTAG UIDs at the same door. It is the usual choice when migrating a site from 125 kHz to 13.56 MHz credentials, because old and new cards both work during the changeover. Check which card types, read modes and output formats each band supports. See 125 kHz vs 13.56 MHz and multi-technology modules.
Dynamic QR code (Rotating QR code, Time-based QR code)
An access QR code that changes over time or per use. A mobile app or management platform generates it with a timestamp or one-time value protected by a signature or encryption, and the reader or controller validates it locally with a shared secret or online with the server. Screenshots and printed copies therefore expire quickly, unlike static QR codes. It is common for visitors, residents and turnstiles. See static vs dynamic QR.

E

EAS (AM 58kHz / RF 8.2MHz) (Electronic article surveillance)
Electronic Article Surveillance: 1-bit anti-theft systems used at retail exits. Acousto-magnetic (AM) systems use 58 kHz resonant labels and hard tags; radio-frequency (RF) systems use 8.2 MHz resonant circuits. An EAS tag is simply active or deactivated and carries no ID, unlike RFID. The two technologies are not interchangeable, and some retailers use UHF RFID tags for the same exit-alarm function. See laundry and garment tags.
Electric bolt lock (Drop bolt, Electric deadbolt)
An electrically operated lock in which a solenoid or motor drives a bolt from a lock body in the frame into a strike on the door edge, or the reverse. It suits glass and frameless doors, including double-swing doors. Many models include a magnetic door-detection sensor so the bolt only throws when the door is closed, plus an adjustable relock delay. Both fail-safe and fail-secure versions exist. See electric bolt locks and types of electric locks.
Electric strike (Door strike, Electric release)
A frame-mounted replacement for a standard strike plate whose keeper (jaw) is released electrically, so the door's latch can pass and the door opens without the latch being retracted. Electric strikes come in fail-safe and fail-secure versions, often field-selectable, and in 12 V or 24 V variants. They keep normal free egress through the door's lever or panic hardware, which makes them a common choice for egress doors. See types of electric locks.
EM4100 (EM4102, TK4100, EM card)
A read-only 125 kHz chip format (EM4100/EM4102, with compatible chips such as TK4100) that transmits a 64-bit factory-programmed code: 9 header bits, 10 rows of 4 data bits each followed by a row-parity bit, 4 column-parity bits and a stop bit. That leaves 40 data bits, often shown as 10 hex digits or as a decimal card number. With no encryption or authentication, it is easily copied to rewritable chips such as T5577. See 125 kHz chips compared.
EM4305 (EM4205)
A read/write LF chip that operates from about 100 to 150 kHz, covering both 125 kHz and 134.2 kHz, with 512 bits of EEPROM in 16 words of 32 bits. Memory includes a factory-set 32-bit unique ID, a configuration word and a 32-bit password for write and lock protection. It supports ISO 11784/11785 FDX-B animal-ID encoding as well as EM4100-style data, so it is common in animal tags and rewritable access cards. See 125 kHz chips compared.
EPC Gen2 (ISO 18000-63) (UHF Gen2, ISO 18000-6C, Gen2v2)
The GS1 EPC UHF Gen2 air-interface protocol for passive UHF RFID, published internationally as ISO/IEC 18000-63 (formerly 18000-6 Type C). It defines reader-to-tag signaling, slotted anti-collision with the Q algorithm, four memory banks (Reserved, EPC, TID, User), inventory sessions S0–S3, and 32-bit access and kill passwords. Gen2v2 added optional cryptographic authentication and privacy (untraceable) features. See tag memory banks and encoding UHF tags.
ETSI 865-868 MHz band (EU UHF RFID band, ETSI EN 302 208)
The main UHF RFID band in Europe, governed by ETSI EN 302 208. Readers transmit at up to 2 W ERP on four high-power channels at 865.7, 866.3, 866.9 and 867.5 MHz within 865–868 MHz. Recent editions of the standard also cover an upper band at 915–921 MHz where national rules permit it. Tags and readers designed for 902–928 MHz may perform worse here, so specify the region. See UHF frequency by country.

F

Facility code (Site code, FC)
A number encoded on a credential alongside the card number that identifies the site or customer a card batch belongs to. It is 8 bits (0–255) in the Wiegand 26-bit format and 16 bits in the common open 34-bit layout. Controllers can reject cards with the wrong facility code, which reduces but does not eliminate duplicate numbers between sites. It is not a security feature: over Wiegand it is sent in the clear. See Wiegand 26-bit.
Fail-safe (Power-to-lock, Fail-open)
A lock that unlocks when power is removed, so the door is free during a power failure or when a fire-alarm relay cuts lock power. Magnetic locks are inherently fail-safe, and many electric strikes and bolt locks can be set this way. Where an electric lock restricts egress, codes such as NFPA 101 generally require release on power loss and fire-alarm activation; confirm with the authority having jurisdiction. See fail-safe vs fail-secure.
Fail-secure (Power-to-unlock, Fail-locked)
A lock that stays locked when power is removed and needs power to unlock. A fail-secure electric strike keeps a door secure from the outside during an outage, while free egress from the inside is provided mechanically by the door's lever or panic hardware. It suits perimeter, storeroom and IT-room doors where local life-safety codes allow it. See fail-safe vs fail-secure and types of electric locks.
FCC 902-928 MHz band (US UHF RFID band, FCC Part 15.247)
The US UHF RFID band under FCC Part 15.247. For FHSS, a 20 dB channel bandwidth below 250 kHz requires at least 50 hopping frequencies and at most 0.4 s occupancy per frequency in 20 s; 250 kHz or more requires at least 25 frequencies and 0.4 s in 10 s. Peak conducted output is limited to 1 W with at least 50 channels, or 0.25 W otherwise, with antenna-gain conditions. Canada uses the same frequency range under separate ISED requirements. See UHF frequency by country.
FDX-B (ISO 11784/11785) (134.2 kHz animal ID, FDX-B animal tag)
The full-duplex animal-identification protocol defined in ISO 11785, carrying the 64-bit code structure of ISO 11784 at 134.2 kHz. The code includes a 10-bit country or manufacturer code and a 38-bit national ID, usually displayed as a 15-digit number, and is used in pet microchips and livestock ear tags. HDX, the half-duplex alternative, carries the same code, and ISO 11785 readers are expected to read both. See livestock ear tags.

H

HDX (half-duplex) (Half-duplex animal ID, ISO 11785 HDX)
The half-duplex animal-ID transmission defined in ISO 11785 alongside FDX-B. The reader powers the tag with a 134.2 kHz field and then pauses; the tag replies during the pause using frequency-shift keying between about 124.2 kHz and 134.2 kHz. HDX carries the same ISO 11784 code as FDX-B and is common in cattle ear tags and some industrial LF systems. See FDX-B and livestock ear tags.
HF (13.56MHz) (High frequency, 13.56 MHz RFID)
The high-frequency RFID band centered on 13.56 MHz, an ISM frequency available worldwide. HF tags couple inductively and follow ISO/IEC 14443 (proximity cards, up to about 10 cm) or ISO/IEC 15693 (vicinity tags, up to about 1 m with large antennas). HF chips offer far more memory and cryptography than 125 kHz chips, covering MIFARE, DESFire, NTAG and NFC credentials. See 125 kHz vs 13.56 MHz.
Holding force (Holding strength)
The rated static pull a powered magnetic lock resists before its armature plate separates, stated in kilograms or pounds, for example 280 kg (600 lb). It is measured with the plate fully seated and pulled straight off the magnet face; real-world resistance falls with misalignment, air gaps, dirt, paint or low supply voltage. Choose a rating that fits the door's use and security level. See magnetic lock buying guide and magnetic locks.

I

IK rating (IK code, IEC 62262)
The impact-protection code for enclosures defined in IEC 62262 (EN 62262), from IK00 to IK10. Each level corresponds to a set impact energy, from 0.14 J at IK01 up to 20 J at IK10, equivalent to a 5 kg mass dropped from 400 mm. Readers and keypads rated IK08 to IK10 are preferred for vandal-prone outdoor or public sites. As with IP ratings, only a tested rating counts. See tamper-proof readers.
Interlock (Mantrap, Access control vestibule, Airlock)
A controller function that links two or more doors so only one can be open or unlocked at a time; the next door stays locked until the previous one is closed, as reported by its door status sensor. Interlocks are used for secure vestibules, cleanrooms, airlocks and cash rooms to prevent tailgating or keep environments separated. Every door in the group needs a door status sensor. See networked door controllers.
Intrinsic safety (Ex ia) (Ex i, Intrinsically safe (IS))
An explosion-protection technique defined in IEC 60079-11 that controls electrical and thermal ignition energy in an assessed circuit. Levels ia, ib and ic have different fault-assessment requirements; the complete equipment marking, conformity evidence and connected system determine suitability for the site's zone, group and temperature conditions. An Ex ia label alone does not approve a reader for Zone 0. Review the documented system or entity parameters, cables and associated apparatus; an external barrier is not a universal add-on, and apparatus inside a classified area needs its own location suitability. See explosion-proof card readers.
IP rating (Ingress Protection code, IEC 60529)
The Ingress Protection code defined in IEC 60529. The first digit (0–6) rates protection against solid objects and dust; the second (0–9) rates protection against water. IP65 means dust-tight and protected against water jets; IP66 adds powerful jets; IP67 covers temporary immersion up to 1 m for 30 minutes. A rating only counts if the product was tested to it, and it says nothing about UV or corrosion resistance. See rain covers.
ISO 14443A/B (ISO/IEC 14443, Proximity card standard)
The ISO/IEC 14443 standard for 13.56 MHz proximity cards, with a typical operating distance up to about 10 cm. Part 1 covers physical characteristics, Part 2 RF power and signaling, Part 3 initialization and anti-collision, and Part 4 a transmission protocol that can carry ISO/IEC 7816-4 APDUs. Type A (used by MIFARE and NTAG) and Type B (used in some ID documents) differ in modulation and bit coding. See 125 kHz vs 13.56 MHz.
ISO 15693 (ISO/IEC 15693, Vicinity card, NFC-V)
The ISO/IEC 15693 standard for 13.56 MHz vicinity cards and tags, designed for longer HF read distances than ISO/IEC 14443, up to about 1 m with a large reader antenna and tag. Tags carry a 64-bit UID and support multi-tag anti-collision, making them common in library, laundry, asset and industrial-tracking applications. Many smartphones read them as NFC-V (NFC Forum Type 5) tags. See industrial HF readers.

K

Key diversification (Diversified keys, Key derivation)
A technique that derives a unique key for each card from a master key plus card-specific data, usually its UID, using a defined algorithm such as the AES-CMAC method in NXP application note AN10922. If one card's key is extracted, only that card is exposed, not the whole system. Readers calculate the diversified key at each tap, often inside a SAM so the master key never leaves secure hardware. See SAM and encrypted readers.
Keyboard emulation (HID) (Keyboard wedge, USB HID keyboard mode)
A USB reader mode in which the reader enumerates as a standard HID keyboard and types the card number, usually followed by Enter, into whichever field has focus. It needs no driver or SDK, so it works with spreadsheets, web forms and point-of-sale software. The trade-offs are one-way communication and output that depends on keyboard layout and format settings. HID here means Human Interface Device, not a brand. See USB reader output formats.

L

LF (125kHz) (Low frequency, 125 kHz RFID)
The low-frequency RFID band (30–300 kHz); access cards use 125 kHz and animal-ID tags 134.2 kHz. LF tags couple inductively, usually reading from a few centimeters to about 10 cm on access-control readers, and are less affected by water than higher bands. Common 125 kHz chips such as EM4100 are read-only and unencrypted, so they are easy to copy. Compare bands in LF vs HF vs UHF.
Liveness detection (Anti-spoofing, Presentation attack detection (PAD))
Checks that confirm a biometric sample comes from a live person at the device rather than a photo, video replay, mask or fake fingerprint. Face terminals may use infrared imaging, depth sensing (structured light or dual cameras) or motion analysis. The formal term is presentation attack detection, with test and reporting methods defined in ISO/IEC 30107-3. Performance varies by device, so ask for test results before specifying. See face recognition guide.
LLRP (Low Level Reader Protocol)
Low Level Reader Protocol: a GS1 (originally EPCglobal) standard for controlling fixed UHF RFID readers over TCP/IP, normally on port 5084. The host configures antennas, transmit power, inventory and access operations, and report triggers, then receives tag reports in a standard binary message format. LLRP lets middleware support readers from different vendors, although vendor-specific extensions are common. See fixed UHF readers.

M

Magnetic lock (Maglock, Electromagnetic lock, EM lock)
An electromagnet mounted on the door frame that holds a steel armature plate on the door while powered, typically at 12 V or 24 V DC. It has no moving parts and is inherently fail-safe, releasing when power is cut. Maglocks are rated by holding force and paired with brackets for different door types. Egress normally requires a REX device and, under most codes, fire-alarm release. See magnetic locks and magnetic lock buying guide.
MIFARE Classic (MIFARE Classic 1K, MIFARE Classic 4K)
An NXP 13.56 MHz memory-card family compliant with ISO/IEC 14443 Type A up to Part 3. The 1K version has 16 sectors of 4 blocks (16 bytes each); the 4K version has 40 sectors. Each sector is protected by two 48-bit keys (A and B) using the proprietary Crypto-1 cipher, which has been publicly broken since 2008, so keys can be recovered and cards cloned. Reading only the UID is weaker still. See MIFARE Classic vs DESFire.
MIFARE DESFire EV3 (DESFire EV3, DESFire)
An NXP 13.56 MHz contactless smart-card chip compliant with ISO/IEC 14443-4 Type A, available with 2, 4 or 8 KB of memory. Data sits in a file system of multiple applications, each with its own keys and up to 32 files. It supports AES-128 (DES/3DES for legacy systems), encrypted and MACed communication, random ID, proximity check against relay attacks, and Secure Dynamic Messaging for NFC taps. It is the usual upgrade path from MIFARE Classic. See MIFARE Classic vs DESFire.
Mobile credential (Mobile access, Phone credential)
An access credential stored on a smartphone or wearable instead of a plastic card, presented to the reader over Bluetooth Low Energy, NFC or a displayed QR code. The access-control platform issues and revokes it remotely, through an app or, where the platform supports it, a wallet pass. The reader must support the same credential scheme as the issuing platform, so interoperability between systems is limited. See Bluetooth controllers.
Modbus (Modbus RTU, Modbus TCP)
An open industrial request/response protocol in which a client (master) reads and writes numbered registers and coils on a server (slave) device. Modbus RTU runs over RS485 or RS232 with a CRC-16 check; Modbus TCP carries the same function codes over Ethernet, normally on port 502. Some industrial RFID readers expose tag data as Modbus registers so a PLC can read it without a custom driver. See industrial HF readers.
Mullion reader (Slim reader, Narrow-profile reader)
A narrow card reader or keypad designed to mount on a door frame or on the mullion (the vertical divider between glass door panels), where a standard wall-box reader will not fit. Its slim housing usually means a smaller antenna and a somewhat shorter read range. Metal frames can detune 125 kHz and 13.56 MHz antennas, so check the product's metal-mounting guidance or use a spacer. See Wiegand card readers.
Multi-technology reader (Multi-tech reader)
A reader that accepts several credential technologies, for example 125 kHz prox, 13.56 MHz MIFARE or DESFire, NFC or Bluetooth mobile credentials and QR codes, and passes them to the controller in a configured output format. It supports mixed card populations and phased migrations. A specification should list each technology exactly, including whether the reader reads only the UID or performs a secure (encrypted) read. See types of card readers.

N

Near-field antenna (Near-field UHF antenna)
A UHF RFID antenna designed to create a strong, tightly confined field close to its surface, typically from a few centimeters to a few tens of centimeters, instead of radiating over meters. It reads tags placed on or just above it, such as items on a counter, tray or shelf or in a smart cabinet, while avoiding stray reads of nearby tags. Small near-field tags often read well only on this kind of antenna. See UHF antennas.
NFC (Near Field Communication)
Near Field Communication: a 13.56 MHz short-range technology, usually working at 4 cm or less, standardized in ISO/IEC 18092 and NFC Forum specifications and compatible with ISO/IEC 14443, ISO/IEC 15693 and FeliCa. NFC devices can read tags, emulate a card or exchange data peer to peer. Because most smartphones include NFC, NFC Forum tags such as NTAG213 and phone-based credentials work with compatible 13.56 MHz readers. See NTAG chips compared.
NO/NC/COM contacts (Normally open, Normally closed, Common)
The three terminals of a changeover relay or switch. COM (common) is the moving contact; NO (normally open) connects to COM only when the relay is energized or the switch is operated; NC (normally closed) is connected to COM at rest and opens when activated. Fail-safe locks such as maglocks are usually wired through COM and NC, and fail-secure strikes through COM and NO. See relay output and wiring diagrams.
NTAG213 (NTAG 213)
An NXP NFC Forum Type 2 tag chip (ISO/IEC 14443 Type A) with a 7-byte UID and 144 bytes of user memory, enough for a URL or short NDEF record. It adds an optional 32-bit password to protect writes (and optionally reads), permanent lock bits, a 24-bit NFC counter and an ECC originality signature. With no encryption, it suits product, marketing and asset links rather than secure access credentials. Compare in NTAG213 vs 215 vs 216.
NTAG424 DNA (NTAG 424 DNA)
An NXP NFC Forum Type 4 tag chip (ISO/IEC 14443-4 Type A) built for authentication. It uses AES-128 keys and Secure Unique NFC (SUN) messages: on each tap it can generate a URL containing the UID and a tap counter, optionally encrypted, plus a CMAC that a server verifies, so copied or replayed URLs can be detected. It has 416 bytes of user memory across its standard files. See NTAG213 vs 215 vs 216 and NTAG424 DNA.

O

On-metal tag (Anti-metal tag, Metal-mount tag)
An RFID tag built to work when mounted directly on metal, which otherwise detunes a tag antenna and disrupts the field. HF and LF designs typically add a ferrite layer, while UHF designs use a spacer or an antenna that treats the metal surface as its ground plane. Read range is quoted for on-metal mounting and often drops off metal. Typical uses are tools, IT equipment, containers and other metal assets. See does RFID work on metal? and on-metal tags.
OSDP (Open Supervised Device Protocol, IEC 60839-11-5)
Open Supervised Device Protocol: a bidirectional protocol between access controllers and peripherals such as readers, published by the Security Industry Association (SIA) and adopted internationally as IEC 60839-11-5. It runs over half-duplex RS485, so one controller can poll several addressed readers on a multidrop bus. It supervises reader presence, drives LEDs and buzzers, and supports AES-128 encryption through Secure Channel. See Wiegand vs OSDP vs RS485 and OSDP Secure Channel.
OSDP Secure Channel (OSDP SC, Secure Channel Protocol (SCP))
The optional encryption layer of OSDP, known as the Secure Channel Protocol (SCP). Controller and reader run a challenge-response handshake to derive session keys from a shared 128-bit Secure Channel Base Key (SCBK), then encrypt message data with AES-128 and add a message authentication code (MAC) to each packet, guarding against eavesdropping, tampering and replay. A published default key (SCBK-D) is meant only for install mode and should be replaced with a unique key. See OSDP.

P

PC/SC (CCID) (PC/SC reader, CCID reader)
PC/SC is the standard API that Windows, macOS and Linux applications use to talk to smart-card readers; CCID is the USB device class that lets such readers run on built-in operating-system drivers. A PC/SC reader exchanges APDUs with the card, so software can authenticate, read and write MIFARE or DESFire data, or run NFC commands, unlike keyboard-emulation readers that only output a number. See USB desktop readers.
PoE (Power over Ethernet) (IEEE 802.3af/at/bt, PoE+)
IEEE 802.3 methods for delivering DC power and data over the same twisted-pair Ethernet cable, up to 100 m. 802.3af (Type 1) guarantees 12.95 W at the powered device, 802.3at (PoE+, Type 2) 25.5 W, and 802.3bt Types 3 and 4 up to 51 W and 71.3 W. PoE controllers, face terminals and fixed UHF readers need no local power supply, but locks may still need separate power. See power supply sizing.
Proximity card (Prox card, 125 kHz card)
In access control, a contactless 125 kHz card or key fob read by holding it near a reader, typically within a few centimeters. It usually carries a fixed ID, such as EM4100-type or HID Prox-compatible data, that the reader passes to the controller as Wiegand output. Prox cards are inexpensive and durable but unencrypted and easy to clone. ISO/IEC 14443 also uses the word proximity for 13.56 MHz smart cards. See cards and key fobs.

R

RAIN RFID (RAIN)
The industry name, promoted by the RAIN RFID Alliance, for passive UHF RFID based on the GS1 EPC Gen2 / ISO/IEC 18000-63 air interface. RAIN is derived from "RAdio frequency IdentificatioN" and reflects the link between tagged items and cloud data. A RAIN-compatible reader or tag works with standard Gen2 equipment in the 860–960 MHz range, within the regional band it is tuned for. See UHF RFID products.
Read range (Read distance, Reading distance)
The maximum distance at which a reader reliably reads a given credential or tag. It depends on frequency, reader output power and antenna, tag chip sensitivity and antenna size, orientation, and surroundings such as metal, liquids and electrical noise. Typical figures are a few centimeters for 125 kHz and 13.56 MHz access cards and several meters for passive UHF tags. Datasheet ranges are usually measured with a specific tag in ideal conditions. See UHF read range.
Relay output (Dry contact output, Lock relay)
A set of switched contacts on a controller, reader or keypad that operates a lock, barrier, alarm or other load. A dry (voltage-free) relay only opens or closes a circuit, so the lock is powered from a separate supply wired through COM and NO or NC; some controllers instead provide a powered (wet) output. Check the contact rating against the lock current, especially for inductive loads. See NO/NC/COM contacts.
Request to exit (REX) (RTE, Exit request)
An input that tells the controller someone is leaving, so it unlocks the door, or at least shunts the door-forced alarm, without a credential. Sources include exit push buttons, passive infrared (PIR) motion sensors above the door and switches in lever or panic hardware. Life-safety codes may also require a manual release that cuts lock power directly, independent of the controller. See exit buttons and wiring diagrams.
RS485 (RS-485, TIA/EIA-485)
A differential serial standard (TIA/EIA-485) that sends data over a twisted pair (A/B) and tolerates electrical noise well. A standard bus supports up to 32 unit loads and runs of up to about 1,200 m (4,000 ft) at lower baud rates; terminate both ends of long runs with 120 Ω resistors. RS485 defines only the electrical layer, so OSDP, Modbus RTU and vendor protocols run on top of it. See Wiegand vs OSDP vs RS485.
RSSI (Received signal strength indicator)
Received Signal Strength Indicator: a reader's measurement of how strong a tag's reply is, usually reported in dBm with each UHF tag read. Software uses RSSI to filter out distant or stray tags, estimate which antenna or zone a tag is nearest, or tune thresholds at portals. It is a relative indicator affected by tag type, orientation and multipath reflections, not a precise distance measurement. See how to choose a UHF reader.

S

SAM (Secure Access Module) (Secure Application Module)
A tamper-resistant smart-card chip, usually a SIM-sized plug-in or a soldered package, installed inside a reader or terminal. It stores cryptographic keys and performs card authentication and key diversification over an ISO/IEC 7816 contact interface, so the reader's main processor never holds the master keys and extracting its firmware does not reveal them. SAM-based readers are common for DESFire and other secure credential schemes. See encrypted card readers.
Standalone access control (Standalone keypad, Standalone reader)
A single-door system in which the reader, user database, decision logic and lock relay are combined in one unit, usually a keypad-reader mounted beside the door. Users are enrolled with a master card, master code or remote control, with no PC or network required. It is inexpensive and simple, but every door is managed separately and audit trails are limited or absent. See standalone keypads and programming guide.
Suppression diode (back-EMF) (Flyback diode, Freewheeling diode)
A reverse-connected diode can suppress the back-EMF voltage spike when a DC coil switches off, protecting contacts and electronics. It also slows current decay and can delay lock release, so it is not a universal addition to magnetic locks. Follow the exact lock and controller manufacturers' suppression instructions, including any built-in protection, specified diode, varistor or other network and its placement. A diode must not be placed directly across an AC coil. Verify release behavior after wiring. See wiring diagrams.

T

T5577 (ATA5577, T5577 blank card)
A rewritable 125 kHz RFID chip with 363 bits of EEPROM organized as 32-bit blocks, each with its own lock bit. Seven blocks (224 bits) hold user data, and one of them can instead serve as a 32-bit password. Its configurable modulation and data rate let it emulate many read-only LF formats, including EM4100, which makes it the usual blank for custom-encoded or replacement 125 kHz credentials. See 125 kHz chips compared.
Tag memory banks (EPC, TID, User) (Gen2 memory banks)
The four memory areas of an EPC Gen2 tag. Bank 00 (Reserved) holds the 32-bit kill and access passwords; Bank 01 (EPC) holds a CRC, Protocol Control bits and the rewritable EPC or item identifier, commonly 96 bits; Bank 10 (TID) holds factory-locked chip-maker and model data and, on most chips, a unique serial number; Bank 11 (User) is optional extra memory whose size depends on the chip. See how to encode UHF tags.
Tailgating (Piggybacking)
When an unauthorized person follows an authorized user through a controlled door before it closes, without presenting a credential; it is often called piggybacking when the authorized user knowingly allows it. A card reader alone cannot detect it. Countermeasures include short unlock times, door-held-open alarms, anti-passback, interlocks, turnstiles or speed gates with optical sensors, and staff awareness. See turnstile and speed-gate readers and anti-passback.
TCP/IP (Ethernet networking)
The Internet protocol suite used by networked controllers, face terminals and fixed UHF readers over Ethernet or Wi-Fi. IP handles addressing and routing; TCP adds reliable, ordered delivery, so devices can talk to management software, SDKs or cloud platforms across a LAN or WAN. Plan a static IP address or DHCP reservation for each device. Application protocols such as HTTP, MQTT and LLRP run on top. See networked door controllers.
TTL/UART (TTL serial, UART)
An asynchronous serial link (Universal Asynchronous Receiver-Transmitter) at logic-level voltages, typically 3.3 V or 5 V, used between RFID modules and a host microcontroller. It needs TX, RX and ground, and commonly runs at 9600 or 115200 baud with 8 data bits, no parity and 1 stop bit (8N1). TTL levels are not RS232-compatible and suit only short, in-enclosure connections, so confirm the module's logic level first. See RFID module selection.

U

UHF (860-960 MHz) (Ultra-high frequency, UHF RFID)
The ultra-high-frequency RFID band. Passive EPC Gen2 (ISO/IEC 18000-63) tags are specified for 860–960 MHz, but each country authorizes a narrower slice, such as 902–928 MHz in the US or 865–868 MHz in Europe. UHF tags reply by backscatter, typically reading at several meters and many tags per second, while liquids and metal reduce performance. See UHF frequency by country.
UID (Unique identifier, Card serial number (CSN))
Unique Identifier: the chip serial number a card or tag reports during anti-collision, set at manufacture. ISO/IEC 14443 Type A UIDs are 4, 7 or 10 bytes, ISO/IEC 15693 UIDs are 8 bytes, and UHF tags usually carry a serial number in their TID bank. Many readers output only the UID, which is fast and needs no keys, but it is not a secret: UID-changeable cards can copy it, and some chips send a random ID instead. Use encrypted reads where security matters. See MIFARE Classic vs DESFire.
Unlock time delay (Relay time, Door open time)
The time a controller, keypad or timer module keeps the lock released after a valid credential or exit request, set in the device's configuration. Too short and users cannot open the door in time; too long and tailgating becomes easier. Some controllers relock as soon as the door status sensor shows the door has opened and closed. It is not the same as delayed egress, a code-regulated feature of some exit locks. See standalone keypad programming.

W

Wiegand (Wiegand interface)
A one-way reader-to-controller interface, named after the Wiegand-effect cards it was created for. Card data travels on two lines, Data 0 (D0) and Data 1 (D1), normally held high (typically 5 V): a low pulse on D0 sends a 0 and a low pulse on D1 sends a 1. It has no encryption, acknowledgment or reader supervision, and runs are generally limited to about 150 m (500 ft). Compare interfaces in Wiegand vs OSDP.
Wiegand 26-bit (H10301) (26-bit Wiegand, Standard 26-bit format)
The most common open Wiegand card format. Its 26 bits are 1 leading even-parity bit, an 8-bit facility code (0–255), a 16-bit card number (0–65,535) and 1 trailing odd-parity bit. The even-parity bit covers bits 2–13 and the odd-parity bit covers bits 14–25. With only 65,536 card numbers per facility code, duplicate cards across sites are possible. Decode one with the calculator in our Wiegand 26-bit guide.
Wiegand 34-bit (34-bit Wiegand)
A Wiegand format with 32 data bits framed by two parity bits: 1 leading even-parity bit covering bits 2–17 and 1 trailing odd-parity bit covering bits 18–33. The open layout splits the data into a 16-bit facility code and a 16-bit card number, but many readers send a 13.56 MHz card's 4-byte UID as the 32 data bits instead. Confirm that reader and controller use the same layout and byte order. See Wiegand reader wiring.

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