How to Read the Numbers on Your Access Card or Fob

The Three Numbers That Matter: Format, Facility, and Card

Every proximity or smart access credential carries at least three distinct identifiers, even if they are not all visibly printed. The format number — sometimes called a part number or format code — describes the bit-length and data structure used to transmit credential data to the reader. Well-known examples include the ubiquitous 26-bit H10301 standard and the proprietary HID Corporate 1000 48-bit format, but dozens of less common formats exist across different manufacturers and installation eras.

The facility code (also called site code) is a number, typically 0–255 in 26-bit systems but potentially larger in extended formats, that identifies a particular site or customer installation. Without it, a replacement card will not work even if the format is correct. The card number is the individual credential identifier within that facility — think of it as the employee or resident number. Facility code and card number together form the logical address the panel checks against its access database.

Where the Numbers Are Printed on Common Cards and Fobs

Proximity cards typically carry markings on the back face. You will usually find a multi-digit part or format number in small print near the top or bottom edge, followed by a hyphenated string showing facility code and card number — for example, '0019 / 04521' or a single hot-stamped string like '012,04521'. Key fobs carry the same data but in a compressed layout; look at the flat face opposite the ring loop, or along the thin edge. Some fobs only hot-stamp a short card number and omit the format code entirely, which is why a physical sample submission is sometimes necessary.

Older systems based on 125 kHz LF proximity technology tend to have the most visible markings, because those formats were designed in an era when installers manually programmed panels. Newer high-frequency smart card formats — including HID Seos and iCLASS variants — may carry less printed data because the credential's logical identity is stored in the chip rather than on the label. For those card types, the printed number is usually a reference label for inventory purposes rather than an encoding parameter.

Indala-format cards are worth special mention: Wiegand-format Indala credentials such as the Indala FlexSecur series often print a full seven- or eight-digit decimal string that encodes both facility and card number within a single value. The format itself is identified by knowing it is an Indala installation, not by a separate printed code. Similarly, Indala ASC 27-bit and Indala Optus 34-bit cards have distinct encoding structures that a supplier must know before producing a compatible credential.

Internal vs External HID Card Numbers

HID proximity cards present a known complication: the number printed on the card face (the external or 'hot-stamp' number) does not always match the number the reader actually transmits to the panel (the internal or encoded number). HID prints an external decimal number for inventory and administrative purposes, but the internal Wiegand data is encoded differently — particularly when the card uses a corporate or proprietary format rather than the standard H10301.

On standard 26-bit H10301 HID cards, the external number is typically a direct representation of the encoded card number, so the two values align predictably. On extended formats like HID H800002 46-bit cards, the mapping is format-specific and the external number is essentially a label that does not decode directly into the panel's expected value. If your installer programmed your panel using the internal encoded number — which is the standard practice — a compatible credential must replicate the encoded data, not just the printed label.

The practical implication: when ordering a compatible HID-format card, you should supply both the printed external number and any programming records your access-control panel holds for that credential. If panel records are unavailable, a supplier with format engineering capability can analyse a submitted sample card to determine the precise encoding. Legacy HID iCLASS Picopass and HID iCLASS Legacy 2K/16K cards use a different number scheme again, where the printed CSN (chip serial number) is read-only and separate from the application data that controls access.

Using the Numbers to Order a Compatible Card

Once you have the format identifier, facility code, and card number, ordering a compatible replacement is straightforward. Supply all three values to your credential supplier. A format-competent supplier will confirm the bit structure, encode a blank credential with the correct facility code and card number, and verify the output data before shipment. For common Wiegand-format cards, this is a routine process; for less common proprietary formats such as ADT 31-bit or Inner Range 36-bit proximity, the supplier needs to confirm format support before accepting the order.

For sites ordering multiple credentials — whether replacing a lost card, expanding an existing installation, or issuing replacements in bulk — the facility code is the critical constant. All credentials on a given site must share the same facility code or the panel will reject them. Card numbers must not duplicate any credential already enrolled in the system, so it is good practice to supply a list of numbers already in use when placing a new order.

If your cards are issued with sequential card numbers, the ordering process is also simpler: provide the format, facility code, and the desired number range. For non-sequential replacements, supply each card number individually. The replacement card ordering process is covered in more detail in our companion guide, which walks through both single-card and bulk replacement scenarios.

When You Cannot Read the Numbers

Not every card or fob arrives with legible markings. Hot-stamp ink fades, labels peel, and some OEM formats were never printed with human-readable data in the first place. In these cases, the most reliable route is to submit a physical sample. A supplier equipped with the right reader hardware can read the raw Wiegand or smart card data off the chip, identify the format from the data structure, and extract the encoded facility code and card number directly.

If you cannot submit a sample — for example, the original credential is lost entirely — check your access-control panel's enrollment records. Most modern panels store the raw credential data read from the fob during enrollment, and a system administrator can export it. Older panels may store only the decoded card number, which is usually sufficient for a 26-bit H10301 format but may be ambiguous for extended formats. In that situation, confirming the format from installation records, the panel manufacturer's documentation, or the reader model is the next step before a compatible credential can be produced.

Sites running less common reader protocols — some older 125 kHz installations, certain regional OEM systems, or multi-technology panels — may need additional information such as the panel model number or the access-control software in use. Providing that context alongside whatever printed data is visible allows a supplier to narrow down the format reliably. Security ID Systems is an independent manufacturer and supplier of compatible access-control credentials and is not affiliated with, authorized by, or endorsed by HID Global, Indala, ADT, Inner Range, or any other access-control system manufacturer referenced on this page.