HID Prox Cards and Fobs: ProxCard II, ISOProx and Other 125 kHz Credentials

Identify

Which HID prox card or fob do I have?

The ProxCard II is a clamshell card (a thicker card built as a sealed plastic shell), up to 0.075 inch thick, with a vertical slot punch as standard. The ISOProx II is the same size and thickness as a standard credit card and can take a slot punched either way.

A thin card with a magnetic stripe, the dark strip a swipe reader reads, is a DuoProx II or a Smart DuoProx II. The Smart ISOProx II and Smart DuoProx II are thin cards made to take a contact smart chip, a chip read through metal contacts on the card face; HID says the chip module is not included.

The ProxCard II, ISOProx II, DuoProx II and ProxKey III carry a number printed on the card, and HID provides a cross-reference list that ties it to the ID number programmed into the credential. HID's brochure adds that most proximity, magnetic stripe and iCLASS credentials bought from HID since Sept 1, 2003 have the sales order number printed on them.

HID's prox brochure lists more, including combination cards that pair HID prox with iCLASS or MIFARE technology; this page doesn't cover them.

For how 125 kHz prox cards differ from 13.56 MHz smart cards on any brand, see prox cards vs. smart cards.

Source HID's product pages and data sheets for each credential, its HID Proximity 125 kHz Cards and Readers brochure and its HID Prox Cards Comparison Chart.

Fobs and tags

Is it a key fob, a sticker tag or a vehicle tag?

The ProxKey III is HID's prox key fob, a pocket-size device that attaches to a key ring, badge clip or lanyard. HID says it suits access control uses where a photo ID is not required.

The MicroProx Tag is a coin-size adhesive disk that turns a nonmetallic card or device into a proximity card. Its data sheet says HID does not claim the tag will work in every situation, and that it is not compatible with the majority of mobile phones.

The ProxPass II is an active tag for vehicle access control, attached with Velcro inside the windshield. HID gives it two to five years of battery life, depending on usage.

Source HID's ProxKey III, MicroProx Tag and ProxPass II product pages, the ProxKey III and MicroProx Tag data sheets, and HID's prox brochure.

Life cycle

Are HID prox cards and fobs still sold?

HID's cards and credentials life cycle page listed the ProxCard II, ISOProx II, DuoProx II, ProxKey III, MicroProx Tag and ProxPass II as General Availability, which HID defines as available for sale, when read on November 10, 2026.

Some variants have ended, including the ProxCard II with an adhesive front and the black MicroProx Tag, both End of Life, which HID defines as no longer available for sale. The Smart ISOProx II and Smart DuoProx II do not appear in the HID Prox list on that page as read on November 10, 2026; their product pages are live.

Source HID's Cards and Credentials Support Life Cycle page.

Read range

How close does the card need to be to the reader?

It depends on both the credential and the reader. HID's data sheets give a typical maximum read range for each pairing and say it is dependent on local installation conditions; the brochure adds that a reader's range also depends on the credential type.

The table uses three HID prox readers: the ProxPoint Plus, a mini mullion reader for a narrow door frame; the ProxPro II, a wall switch reader; and the MaxiProx, a long range reader.

HID's documents disagree on four of the figures in the table, and it gives both: the ProxCard II at the MaxiProx, the MicroProx Tag at the ProxPro II and at the MaxiProx, and the ProxPass II's range.

Source Each credential's data sheet, HID's prox brochure and comparison chart, and the ProxPoint Plus, ProxPro II, MaxiProx and ProxPass II product pages.

Formats

What is a card format, and why does it matter?

A format is the structure of the data stored in a card: a string of bits that the access control system turns into a card number. HID's brochure calls knowing the format critical to program and order any credential, because some formats are unique to particular access control systems.

The ProxCard II, ISOProx II, DuoProx II and ProxKey III support formats up to 85 bits, with over 137 billion codes. The MicroProx Tag holds up to 84 bits, and the ProxPass II product page says it takes any HID format up to 37 bits.

HID describes formats as open, tracked or restricted, and the table gives the four its brochure explains. The brochure says not all access control systems can handle the 37-bit formats, and some cannot handle the 35-bit one.

Source HID's prox brochure, the ProxCard II, MicroProx Tag and ProxPass II product pages and data sheets, and HID's PACS Security Guidelines.

Readers

Which HID readers read them?

HID's data sheets say the ProxCard II, ISOProx II, DuoProx II, ProxKey III and MicroProx Tag work with all HID proximity readers. The ProxPass II is the exception: it is solely compatible with the MaxiProx reader.

HID's readers life cycle page listed the readers under its HID Prox Readers heading as General Availability on November 10, 2026, among them the EntryProx, MaxiProx, MiniProx, ProxPoint Plus, ThinLine II and the gray ProxPro II, with a note that European customers should contact their representative for availability. The beige, white and black ProxPro II are listed as End of Sales, with a last time buy date of Aug 31, 2024 and an end-of-life date of Dec 31, 2024; HID names HID Signo or the gray ProxPro II as the migration path.

HID says its iCLASS SE, multiCLASS SE and Signo readers can operate in migration mode, which permits more than one credential type so newer cards can be phased in to existing systems. It strongly recommends that legacy credentials, such as prox cards, are disabled once the upgrade phase is complete.

Those readers' models and the cards each one lists are on the HID card readers page.

Source Each credential's data sheet and product page, HID's prox brochure, its Readers and Encoders Product Support Life Cycle page and its PACS Security Guidelines.

Security

How secure is HID Prox, and what does HID say about moving off it?

HID's PACS Security Guidelines describe prox as credentials with no security at all.

HID also says prox can be practical for some organizations, especially those facing minimal security threats or with other protective measures in place. It compares that choice to door keys that can be duplicated at the local hardware store, and says it continues to serve the needs of customers choosing to rely on legacy products.

For moving off prox, HID recommends that users of legacy credentials upgrade to more modern and higher security credentials like HID Seos. During the changeover, migration mode lets both kinds work; HID recommends a hard cut-off date communicated to credential holders, and disabling legacy credential support once the migration is complete.

HID calls printed card numbers sensitive information and says credential numbers serve the same purpose as a password. Cards can be ordered without a printed number, or with a non-matching one that differs from the number encoded inside.

On formats, HID says that with open formats such as the 26-bit H10301, it is possible for malicious individuals to order credentials with values that could be found in existing systems. It recommends restricted or tracked formats unless needed for compatibility, for organizations outside its HID Elite Program, which HID designed for customers who want full control of dedicated and unique credential and reader authentication keys.

Source HID's PACS Security Guidelines executive brief.

FAQ

HID Prox card and fob questions

Help with HID prox cards and fobs in the Bay Area

Elwin Security installs, repairs and supports card reader and key fob systems that use HID prox credentials through its card reader and key fob access control service for commercial and multifamily properties in the San Francisco Bay Area. Calls are answered 8:00 AM-8:00 PM daily at (408) 539-0535.