HID cards are contactless access control credentials that use radio frequency identification (RFID) to unlock doors without a key. When you hold an HID card near a reader, the card sends a unique ID code, the access control system checks that code against its list of approved credentials, and the door unlocks in under a second. HID Global makes these cards in several families, from legacy 125 kHz proximity cards to encrypted 13.56 MHz smart cards and mobile credentials that live on a phone. This guide covers how HID cards work, the main card types, the readers that pair with them, mobile access, and the security trade-offs that decide which credential fits your building.
Key Takeaways
- HID cards use RFID to send a unique ID code to a reader, which the access control system checks before unlocking the door in under a second.
- Frequency sets the security level. Legacy proximity cards run at 125 kHz with no encryption, while iCLASS and Seos smart cards run at 13.56 MHz with encrypted communication.
- Four HID card families cover most buildings: iCLASS Seos (encrypted and mobile-ready), iCLASS SE (secure smart card), iCLASS (versatile multi-technology), and Crescendo (FIPS-certified for government).
- The reader has to match the card. HID Signo and multiCLASS SE readers read several card technologies at once, which is what lets an organization upgrade old cards without replacing every door on the same day.
- Legacy 125 kHz cards can be cloned with inexpensive tools, and even the encrypted iCLASS SE line was shown vulnerable in 2024. Seos credentials and mobile access are the more secure path forward.
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What Is an HID Card?
An HID card is a plastic access credential with an embedded RFID chip and antenna that identifies the cardholder to a reader. It contains three core parts:
- A physical casing, usually PVC or thicker clamshell construction
- An antenna coil that receives and transmits signals
- An embedded integrated circuit, the RFID chip
The chip is what makes the card useful for access control. It stores the credential data and communicates with the reader mounted at a door, gate, or turnstile. Unlike a metal key, an HID credential can be programmed, reassigned, or switched off remotely through your access control software, so a lost card becomes a two-minute fix instead of a lock change.
HID cards do more than open the front door. Each credential can carry different access privileges, so an interior door to a server room or pharmacy can be set to open only for staff whose cards hold that permission. Because the system logs every card read, facility managers get an audit trail of who opened which door and when. Many HID cards also print a facility code and cardholder photo on the outside, which lets one credential double as a photo ID badge.
HID makes the same technology in several form factors beyond the standard card, including key fobs and adhesive tags. We install and configure the full range through our HID access control systems, and the card is only one half of the system. The reader it talks to is the other half. See our guide to proximity reader access control for how the two work together.
How Do HID Proximity Cards Work?
HID proximity cards work by drawing power from the reader’s electromagnetic field, then broadcasting a stored ID code back over radio waves. No battery and no physical contact are involved. The full handshake happens in five steps:
- Reader activation. The reader constantly emits a low-power electromagnetic field, at 125 kHz for standard proximity cards or 13.56 MHz for high-frequency smart cards.
- Card energization. When the card enters that field, its antenna coil absorbs enough energy to power the chip.
- Data transmission. The powered chip sends its unique ID code back to the reader over radio waves.
- Verification. The reader passes the ID to the access control system, which checks it against the database of authorized credentials.
- Access decision. If the ID is valid, the system releases the door lock.
The whole sequence takes less than a second, which is why proximity cards suit high-traffic entrances where people would back up behind a keypad. Standard HID proximity cards have a typical read range of 3 to 6 inches, though some reader configurations extend that to around 24 inches, and long-range vehicle readers such as the HID ProxPass line can reach several feet for parking gates.
The ID code is not random. On a legacy proximity card, the reader converts the card’s signal into the Wiegand format and passes it to the controller, which reads a facility code and a card number out of it. The most common layout is the 26-bit H10301 format, and HID proximity technology also supports higher-bit formats, up to 85 bits, for organizations that need a larger pool of unique credentials. That format is also the weak point. A 125 kHz card transmits its facility code and card number in the clear, with no encryption, which is what makes legacy cards easy to copy.
HID Card Types Explained
HID makes four main card families, and the technology inside each one, low-frequency or high-frequency, decides how secure it is and which readers can read it. The comparison below sets those four families against the legacy proximity card they replace, and each of the four families is detailed underneath.
| Card family | Frequency | Security | Best suited to | Status |
|---|---|---|---|---|
| iCLASS Seos | 13.56 MHz | Highest. AES-128 encryption, mutual authentication | Organizations that want one credential for doors, IT login, and mobile | Current, recommended |
| iCLASS SE | 13.56 MHz | High. Encrypted, uses HID’s Secure Identity Object data model | Secure sites that may add mobile later | Current |
| iCLASS | 13.56 MHz | Moderate to high. Encrypted, widest reader compatibility | Mixed environments upgrading from older readers | Current |
| Crescendo | 13.56 MHz | Highest, government-grade. FIPS 201 / FIPS 140-2 certified | Federal agencies and contractors under compliance mandates | Current |
| Legacy Prox (ProxCard II) | 125 kHz | Lowest. No encryption, clonable | Older systems awaiting migration | Legacy, being phased out |
iCLASS Seos
iCLASS Seos is HID’s most secure credential and the one built for mobile access. It uses AES-128 encryption and mutual authentication, so the card and reader each prove their identity before any data moves. A Seos credential is not tied to a single piece of plastic. It can be issued to a card, a fob, or a smartphone, which lets one identity open a door and log into IT resources. Seos also supports one-time password and two-factor workflows for organizations that secure digital systems as tightly as physical ones.
iCLASS SE
iCLASS SE is a high-frequency 13.56 MHz smart card that encrypts the data exchanged with the reader. It stores credentials inside HID’s Secure Identity Object model, which makes duplication far harder than a legacy proximity card. The SE platform works across a range of entry points, from perimeter gates to interior turnstiles, and it is a common choice for organizations that want a secure card today and the option to add mobile credentials later on the same readers.
iCLASS
iCLASS is the versatile, widely compatible member of the family. It runs at 13.56 MHz with encrypted communication, and many iCLASS cards also carry a magnetic stripe or a second technology so they work with both new smart-card readers and older infrastructure. That backward compatibility makes iCLASS a practical bridge for facilities running a mix of reader types or upgrading their access control in phases.
Crescendo
Crescendo is HID’s government-grade credential line. Like Seos, it handles both physical door access and digital login, using encryption and digital signatures for high-assurance environments. Crescendo PIV cards are FIPS 201 compliant and NIST FIPS 140-2 Level 2 certified, and they appear on the GSA FIPS 201 Approved Products List, which federal agencies and their contractors are required to buy from. Newer Crescendo cards combine FIDO2, PKI, and physical access on one credential, and the latest Crescendo 4000 is in validation for the newer FIPS 140-3 Level 2 standard. If your facility has to meet federal identity mandates, Crescendo is usually the specified card.
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HID Card Readers
An HID card only works with a reader that speaks its technology, so the reader choice matters as much as the card. HID’s current readers are built to read more than one credential type, which is what makes a phased upgrade possible. The three you will see most often are:
- HID Signo readers support the widest set of credentials, including Seos, iCLASS SE, iCLASS, and common MIFARE smart cards, plus mobile credentials over both Bluetooth and NFC. Signo readers also support Apple Wallet employee badges.
- multiCLASS SE readers read legacy 125 kHz proximity cards and 13.56 MHz smart cards at the same time, along with mobile. This is the workhorse for organizations moving off old Prox cards, because it reads the old and new credentials during the transition.
- iCLASS SE readers focus on encrypted 13.56 MHz smart cards and mobile, for sites that have already standardized on secure credentials.
Reader and card compatibility is the detail that trips up most upgrades. A reader that only reads 13.56 MHz will not read a 125 kHz Prox card, so replacing cards without checking the readers, or the reverse, leaves doors that do not open. The safe path is a multi-technology reader such as Signo or multiCLASS SE, which reads the old credential and the new one until every card is reissued.
Modern readers also change how they wire back to the controller. Older readers use the one-way Wiegand protocol, while current HID readers support OSDP (Open Supervised Device Protocol), which adds encryption between the reader and the controller and reports tampering. For a deeper look at reader options, see our guides to proximity reader access control and the different types of access control readers.
HID Mobile Access and Mobile Credentials
HID Mobile Access replaces the physical card with a credential stored on a smartphone, so an employee’s phone becomes the badge. The credential is powered by Seos, the same encrypted architecture used in iCLASS Seos cards, and it is issued and revoked through a management portal instead of by handing out plastic. Staff hold the phone near a compatible reader over Bluetooth or NFC, and the door opens the same way a card would.
Mobile credentials solve two problems cards create. Issuing and revoking access no longer requires printing or collecting a card, and phones are less likely to be shared or lost than a badge. HID mobile credentials can also live in Apple Wallet and Google Wallet on supported readers, so there is no separate app to open at the door.
Choosing between cards, fobs, and mobile is a system decision, not just a credential swap, because it depends on your readers, your access control platform, and how your team actually moves through the building. We are brand-agnostic on the platform behind mobile access and specify what fits the site rather than defaulting to one product.
Are HID Cards Secure? Cloning and the 2024 Disclosure
HID card security depends entirely on the technology inside the card. Legacy 125 kHz proximity cards, including the widely used ProxCard II, transmit a fixed facility code and card number with no encryption. An inexpensive off-the-shelf reader-writer can capture that data and produce a working duplicate, which is why security teams treat legacy Prox as convenient but not secure.
Encrypted 13.56 MHz credentials raise the bar substantially. iCLASS SE and Seos use encryption and mutual authentication, so a reader cannot simply copy the data off the card. Even so, encryption is not a permanent guarantee. In August 2024, researchers presented findings at the DEF CON 32 security conference showing they could extract the authentication keys from HID’s iCLASS SE encoders, the devices that program keycards. Because those keys could then be reused, the technique made it possible to clone iCLASS SE cards with common RFID tools. The disclosure was reported by Wired and the security-industry outlet IPVM, and HID issued guidance and updates in response.
The practical takeaway is direction, not panic. Legacy 125 kHz cards should be replaced with encrypted credentials. Encrypted systems should be kept patched, use current key management, and lean toward Seos or mobile credentials, which carry the strongest protections HID offers. Unauthorized duplication of a credential you do not own or control is both a security risk and, in most cases, against the law, so the goal here is understanding your exposure, not copying cards.
Which Industries Use HID Cards?
HID cards appear across nearly every industry that needs to control who enters a building and when. Common deployments include:
- Corporate offices for employee building and floor access
- Healthcare facilities to secure patient areas, records rooms, and pharmaceutical storage
- Schools and universities for building access and combined student ID badges
- Government facilities that require FIPS-compliant credentials such as Crescendo PIV
- Manufacturing plants and warehouses that need durable, longer-range credentials
- Multi-tenant and multi-site buildings managing access across separate organizations
As a commercial security installer, we design and configure HID access control for both commercial businesses and public-sector organizations, and the right card differs between them. A commercial office may standardize on Seos cards or mobile credentials for convenience and easy reissue, while a federal contractor is often required to use FIPS-certified Crescendo cards. Safe and Sound Security has installed HID equipment for more than 80 customers across 160-plus signed deals, and we build each system around the compliance rules and daily traffic of the specific facility.
Key Benefits of HID Card Systems
An HID card system delivers advantages that physical keys and basic locks cannot match:
- Contactless entry speeds people through doors and avoids the wear of swipe or keyed locks
- Centralized control lets administrators grant or revoke a credential instantly from software
- Audit trails record every card read for security reviews and compliance
- Scalability across more doors, buildings, and sites without re-keying
- Integration with video surveillance, alarms, and visitor systems for one connected security picture
Frequently Asked Questions
What is a HID card?
A HID card is a contactless access control credential made by HID Global that uses an embedded RFID chip to identify the cardholder to a reader. Holding the card near a reader sends a unique code to the access control system, which unlocks the door if the code is authorized. HID cards come in low-frequency 125 kHz proximity versions and more secure high-frequency 13.56 MHz smart-card versions.
What is the difference between RFID and HID cards?
RFID is the underlying technology, and HID cards are one brand that uses it. RFID (radio frequency identification) describes any system where a chip transmits data to a reader over radio waves, and it covers everything from inventory tags to toll transponders. HID cards are access control credentials from HID Global built on RFID, in both 125 kHz proximity and 13.56 MHz smart-card forms. So every HID card is an RFID device, but not every RFID device is an HID card.
Can HID proximity cards be cloned or copied?
Standard 125 kHz HID proximity cards can be cloned because they transmit a fixed facility code and card number with no encryption, and cheap reader-writers can duplicate them. Higher-security credentials such as iCLASS SE, Seos, and Crescendo use encryption that makes copying far harder, though a 2024 disclosure showed even iCLASS SE encoders could be compromised under specific conditions. Organizations worried about cloning should move off legacy Prox to encrypted or mobile credentials and keep their systems patched.
How do I tell what type of HID card I have?
Check the printing on the card and the format numbers, which usually indicate the technology. Legacy proximity cards often carry names like ProxCard II and run at 125 kHz, while iCLASS, iCLASS SE, Seos, and Crescendo are printed on the higher-security 13.56 MHz cards. If the markings are unclear, a multi-technology reader or your access control provider can identify the card’s frequency and format, which matters when you order replacements or plan an upgrade.
How much does an HID card cost?
An individual HID card typically costs only a few dollars, but the number that matters for a business is the full access control system, not the blank card. Total cost depends on the number of doors, the readers, the controllers, the software, and installation. For a breakdown of what a commercial system costs, see our guide to access control system cost.
How long do HID cards last?
HID cards typically last 3 to 5 years or longer under normal use. Because they have no battery, the reader’s field powers them, so lifespan comes down to physical wear, environmental exposure, and how often the card is used. Thicker clamshell cards tend to outlast thin printable ISO cards.
Do HID proximity cards need batteries?
No. HID proximity cards are passive RFID devices with no battery. The reader’s electromagnetic field powers the card’s chip long enough to transmit its ID code, so there is nothing inside to charge or replace.
The Bottom Line
HID cards remain one of the most practical ways to control access to a commercial building, and the choice that matters is the technology inside the card, not the plastic itself. Legacy 125 kHz proximity cards are convenient but clonable, while encrypted 13.56 MHz credentials like iCLASS SE and Seos, and mobile access on a phone, offer the security most organizations now need. The reader has to match the card, which is why an upgrade is a system decision rather than a card swap.
As a commercial security installer serving businesses and government agencies nationwide, Safe and Sound Security designs, installs, and manages HID access control systems around each facility’s compliance requirements and daily traffic. If you are planning a new system or moving off legacy cards, talk to our access control installers about the credential and reader mix that fits your building.
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