Keri Systems Cards Explained: K-format, MS / Megastar & NXT

Who Keri Systems Is and Which Panels Use These Cards

Keri Systems is a US access-control manufacturer best known for its PXL-series intelligent controllers — the PXL-250 (single-door), PXL-500 Tiger (multi-door), and the software-defined Doors.NET platform. These panels are widely deployed in corporate offices, healthcare facilities, schools, and light-industrial sites across North America, often installed in the late 1990s through 2010s and still running reliably today.

Because Keri sold complete turnkey systems — panel, software, and credential — their readers are factory-configured to accept only credentials encoded in Keri's own proprietary formats. A standard 26-bit Wiegand card from a generic supplier will not present correctly at a Keri reader. This is not a fault of the installation; it is simply how the system was designed, and it is the primary reason sourcing replacement credentials requires a supplier who has documented the Keri format family in full.

Keri sits within a cluster of legacy US proprietary prox systems — alongside AMAG, Lenel, Kantech, and GE — that issue cards in formats the major prox-blank distributors never stocked as off-the-shelf compatibles. If you are managing an older Keri installation and need new credentials, understanding which generation your readers use is the essential first step.

K-Format / MS (Megastar) Proprietary Prox Decoded

The original Keri credential is a 125 kHz passive proximity card or fob built around a proprietary encoding Keri refers to internally as K-format, and which appears on packaging and datasheets as MS or Megastar. Like most proprietary LF prox formats of its era, it transmits a fixed binary string on power-up from the reader's RF field — but the bit structure, parity scheme, and modulation are specific to Keri, not the industry-standard 26-bit H10301 layout that generic cards use.

The physical credential is a standard CR80 card (85.6 × 54 mm) or ISO key-fob form factor, visually indistinguishable from a generic proximity card. Inside, a passive coil and chip store the encoded data; there is no battery and no active transmission. The chip communicates via PSK (phase-shift keying) modulation, which is one of the standard LF modulation schemes alongside FSK and ASK used across the 125 kHz LF proximity landscape.

A compatible Keri MS proximity card is produced on a programmable LF blank — specifically the T5577 or EM4305 family of chips, which are the industry-standard substrates for producing compatible versions of documented proprietary LF formats. The T5577 is a multi-protocol programmable blank that can be configured to output virtually any LF bit stream once the target format's encoding parameters are known. The credential arrives pre-encoded with your facility code and card number range and reads at Keri readers exactly as an original Megastar card would.

Keri NXT: The 13.56 MHz MIFARE Generation

Keri introduced the NXT credential line to bring higher-frequency smart-card technology to their platform. NXT cards operate at 13.56 MHz and are built on genuine NXP silicon — specifically MIFARE Classic 1K in the base NXT-C variant. This places them in the high-frequency smart-card category alongside credentials from many other access-control manufacturers that migrated away from 125 kHz in the 2010s.

The NXT platform encodes access data in MIFARE sectors using Keri's own key and data structure rather than a generic application layout. This means a blank MIFARE Classic 1K card purchased from a component distributor will not work at an NXT reader without being encoded in the correct Keri sector format. A compatible Keri NXT-C proximity card is produced on genuine NXP MIFARE Classic 1K stock, encoded with the correct sector layout, key structure, and your facility-specific card data.

It is important not to conflate the NXT and MS/Megastar lines. Many Keri installations that were upgraded or expanded in the 2010s have a mixed estate — some doors running PXL readers configured for K-format prox, others fitted with NXT readers. Before ordering replacement credentials, confirm which reader model is installed at each door; the two formats are not interchangeable, and NXT readers will not accept K-format cards or vice versa. Our card format identification guide walks through how to confirm which technology your readers are looking for.

How a Compatible Keri Credential Is Produced

Producing a compatible credential for any proprietary access-control system requires three things: an accurate, complete documentation of the format's encoding parameters; appropriate programmable blank stock; and controlled encoding equipment. For the K-format / MS line, the blank is a T5577 or EM4305 chip programmed to output the Keri PSK bit stream with correct parity and data structure. For the NXT line, the blank is genuine NXP MIFARE Classic 1K stock encoded into Keri's sector layout.

The credential you receive is a finished, field-ready card or fob — not a blank that requires further programming on-site. It contains your specific facility code and the card numbers you specify, formatted exactly as a Keri reader expects. There is no reader reprogramming, no firmware update, and no enrolment database change required: simply present the new card to the reader and it operates normally within whatever access levels that card number holds in your Doors.NET or PXL panel.

This is the core value of sourcing from a specialist supplier who has invested in documenting the Keri format family. Generic access-card suppliers and many locksmith trade accounts carry only standard 26-bit H10301 prox stock — which is useless at a Keri reader. The difference between a compatible credential and a standard prox blank is the encoding, and that encoding requires format-specific knowledge that is simply not widely distributed in the industry. For a broader look at what distinguishes a compatible credential from a generic one, our compatible vs genuine access cards guide covers the subject in detail.

What to Send Us to Order a Compatible Keri Replacement

Ordering compatible Keri Systems proximity cards requires a small amount of information that your existing credentials or panel software will already contain. For K-format / MS cards, we need the facility code (also called site code) printed on the card or retrievable from your Doors.NET or PXL controller software, plus the card number range you need encoded. Most Keri installations use a 26-bit-class proprietary data structure with a discrete facility code field; if you are unsure, a card from your existing stock will confirm it when read.

For NXT credentials, the same basic information applies: facility code and card number range. Because NXT cards carry data in MIFARE sectors rather than a simple LF bit stream, the sector key and data layout must match your installation's configuration. In practice, this means we encode to the standard Keri NXT format that all standard Doors.NET and NXT reader firmware expects — unless your installation has been customised, which is uncommon in field deployments.

If you are uncertain whether your site uses K-format, NXT, or a mix, photograph the reader model number (usually on a label inside the reader housing) and include it with your enquiry. We can cross-reference the reader model to the credential type it accepts and confirm the correct product before you order. For facilities managing a mixed estate of Keri and other legacy systems, we also supply compatible credentials for Lenel 42-bit, Avigilon, Vicon VAX, and Software House CCOTZ 37-bit installations, so a single order can cover multiple panel types. Contact us with your details or browse our full compatible credential catalogue to get started.

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