Lenel Cards Explained: 26-bit, 37-bit & the Lenel 42-bit Format

Lenel, LenelS2 and OnGuard: The Landscape

Lenel Systems International developed the OnGuard platform as a unified access control and security management system, and over successive ownership changes the brand became LenelS2 — the name used today across sales, documentation, and hardware part numbers. Despite the rebranding, the underlying reader infrastructure and the card formats it supports remain consistent across generations of OnGuard deployment.

OnGuard is a software-centric platform: the access control panel, the reader heads, and the card credentials are treated as interchangeable components connected by the Wiegand interface. That architecture means the card format matters more than the specific card part number — two cards from entirely different manufacturers will both work in the same Lenel reader as long as they transmit identical bit strings. This is the technical basis on which Lenel compatible proximity cards are supplied as drop-in replacements for site expansions and lost-card replacements.

Facilities managers operating large or multi-site OnGuard deployments frequently encounter a mix of format generations. Cards issued in the early 2000s may carry plain 26-bit data while panels installed after major upgrades may be enrolled against 37-bit or 42-bit databases. Knowing how to read the printed facility code and card number from an existing credential — and which bit layout governs how those numbers are encoded — is practical knowledge for any Lenel site administrator.

Standard 26-Bit and 37-Bit Lenel Deployments

The 26-bit H10301 format is the most widely deployed Wiegand structure in North America, and Lenel OnGuard readers have supported it from the platform's inception. The structure is straightforward: 1 even-parity lead bit, an 8-bit facility code (values 0–255), a 16-bit card number (values 0–65,535), and 1 odd-parity trailing bit, for 26 bits in total. Because facility codes are limited to 8 bits, large organisations often exhaust their number space, and card number collisions between different facilities sharing the same code are a recognised operational risk.

The 37-bit format extends both fields significantly. One common 37-bit variant allocates a 16-bit facility code and an 18-bit card number, giving far larger address spaces before collisions occur. Lenel panels enrolled against 37-bit databases will reject 26-bit cards carrying the same raw number, since the reader decodes the bit stream before comparing it to the credential database — the physical card technology (ISO card, key fob, thin card) is irrelevant to this check. Both 26-bit and 37-bit Wiegand bit-format credentials are standard catalogue items that require only your facility code and card number range to produce.

If you are unsure which format your site runs, the How to Identify Your Access Card or Key Fob Format guide walks through the practical steps: checking the panel software's credential record, reading the card data with a Wiegand analyzer, and interpreting the number printed on existing cards. Most Lenel installations that have not been custom-configured will be running one of these two standard formats, making compatible card sourcing straightforward.

The Proprietary Lenel 42-Bit (L11601) Format Decoded

The 42-bit format associated with Lenel L11601-series hardware is the format most likely to create sourcing difficulties, because it falls outside the standard Wiegand catalogue stocked by general proximity card distributors. Its bit layout is: 1 leading even-parity bit, a 14-bit site code (values 0–16,383), a 12-bit card number (values 0–4,095), and 1 trailing odd-parity bit, totalling 42 bits. The expanded site code field is the practical advantage: a 14-bit site code supports more than 16,000 distinct facility values, which is meaningful for large enterprise and campus deployments where 26-bit address exhaustion is a real constraint.

Encoded onto a 125 kHz LF substrate, the 42-bit data stream is transmitted over the standard Wiegand interface in the same way as any other format — the reader simply decodes a longer bit string. Because the site and card fields are different widths than in H10301, a reader configured for 42-bit operation will not accept a 26-bit card even if the facility code values happen to overlap numerically. This is also why sourcing the correct replacement matters: a generic 26-bit card ordered without verifying the installed format will be silently rejected at every reader.

The Lenel 42-bit compatible card requires three pieces of information to produce correctly: the total bit width (42), the site code as stored in the OnGuard database, and the desired card number range. With those three parameters confirmed, a compatible credential encodes identically to an OEM-sourced card and presents the same Wiegand output to the reader. The Complete Wiegand Format Guide covers the parity logic and field boundaries in full for facilities staff who need to verify encoding accuracy.

How a Compatible Lenel Card Is Encoded

All low-frequency 125 kHz proximity cards — regardless of brand or format — store their data on a rewritable LF transponder chip. The 125 kHz LF proximity card substrate used in compatible Lenel credentials is a T5577 or EM4305 rewritable chip, programmed at the factory with the exact bit pattern the Lenel reader expects. The chip itself does not carry any brand association; the format is entirely defined by the bit structure written to it.

Encoding a compatible card for a Lenel 42-bit site means computing the correct parity bits, assembling the full 42-bit string in the correct field order (parity, site, card, parity), and writing that string to the chip in the correct modulation and data rate for EM/HID proximity compatibility. Encoding a 26-bit or 37-bit card follows the same process with shorter field widths. The Lenel 42-bit compatible proximity card is factory-encoded to your specified site code and card number range — it is not a blank that requires on-site programming.

Smart card formats used in higher-security Lenel environments — typically MIFARE DESFire or Lenel's own MIF-based credentials — operate differently. These are blank smart credentials that your OnGuard system enrols using its own site-specific encryption keys. The credential does not carry the keys at the point of manufacture; the system writes them during the enrolment process. This is the correct framing for any encrypted smart-card format: the credential is a compatible blank that your own access control system commissions, not a pre-programmed replica. See the Corporate 1000, FlexSecur and Custom Facility Codes guide for additional context on how proprietary encoding schemes are handled at the system level.

Ordering Compatible Lenel Credentials in Bulk

Site expansions, employee onboarding surges, and lost-card replacements all create demand for compatible Lenel credentials outside normal OEM supply channels. The information required to place a bulk order is the same regardless of format: the bit width (26, 37, or 42), the site or facility code, the card number range required, and the physical form factor (ISO card, clamshell, or key fob). If the bit width is not recorded in the system documentation, it can usually be retrieved from the OnGuard credential record or confirmed by reading an existing card.

The AMAG Lenel Kantech compatible prox card listing covers several platforms that share compatible physical and electrical specifications, which is relevant for multi-vendor sites where a single card stock needs to work across more than one access control platform. For sites that have encountered the specific L11601 part number in legacy documentation, the Lenel L11601 36-bit compatible card covers that variant of the extended format family.

Lead times for standard 26-bit and 37-bit Lenel cards are typically short, as these are high-volume catalogue formats. The 42-bit format requires factory programming to your specific site and card number parameters and ships as finished, enrolment-ready credentials. For facilities operating mixed-format environments — common where OnGuard has been deployed in phases over many years — compatible cards can be ordered across multiple formats in a single engagement, each batch programmed to the correct bit layout for that reader group. Contact our technical team to confirm your format requirements before placing a bulk order.

Security ID Systems is an independent manufacturer and supplier of compatible access-control credentials and is not affiliated with, authorized by, or endorsed by Lenel Systems International or LenelS2.