Indala Format Numbers Explained: FlexSecur, 26/27/29-bit & Optus

Indala and PSK Encoding: Why It Isn't HID Prox

Standard HID Prox credentials broadcast using frequency-shift keying (FSK), toggling between two carrier frequencies to represent binary data. Indala uses phase-shift keying instead, representing bits by inverting the phase of the 125 kHz carrier. The practical effect is that an Indala reader's demodulator is tuned for phase transitions, not frequency shifts — placing the two product lines in separate, non-interchangeable ecosystems despite sharing a carrier frequency and a parent company.

This distinction matters when sourcing replacements. A facility running 125 kHz LF proximity cards across a mixed estate needs to identify not just the frequency but the modulation scheme before ordering. PSK modulation is also used by a small number of other legacy formats, so the presence of 125 kHz alone is not sufficient to confirm Indala compatibility. The definitive indicator is the specific card or reader part number from your installation documentation.

On the credential side, the PSK waveform is reproducible on a T5577 or Q5 programmable blank. The T5577 programmable blank can emulate PSK modulation when its configuration registers are set correctly, which is why T5577-based blanks are the standard substrate for compatible Indala credentials across most bit-width variants in the format family.

The Indala Format Family: 26-bit, 27-bit, 29-bit, Optus 34-bit, and DSX 33-bit

The original Indala card format — catalog reference 40134 — uses a 26-bit frame that superficially resembles the Wiegand 26-bit standard but is encoded in PSK rather than Wiegand pulse-width modulation. This means that while the data payload (8-bit facility code, 16-bit card number, two parity bits) follows a familiar layout, the on-card encoding is entirely different. A compatible Indala compatible proximity card for a 40134 installation must be programmed with PSK modulation, not Wiegand pulse encoding.

The ASC 27-bit variant adds a single extra bit to the standard frame, expanding either the facility code or card number field depending on the specific implementation. The Indala ASC 27-bit compatible card is one of the more commonly encountered variants in North American commercial installations from the late 1990s through mid-2000s. The Indala 29-bit compatible prox card extends the credential space further and is associated with larger enterprise deployments requiring more card numbers per facility code.

Optus 34-bit was developed for telecommunications infrastructure and utility sector access control in Australia and is still active in legacy installations across the region. The Indala Optus 34-bit compatible card carries a larger card number field, supporting populations that exceed the limits of 26-bit or 27-bit frames. The DSX 33-bit variant is closely associated with DSX Access Systems panel deployments; the DSX 33-bit Indala compatible card is typically ordered when DSX panel documentation confirms Indala PSK encoding on that specific reader hardware.

FlexSecur: Scrambled Facility Codes Explained

FlexSecur is an Indala option that applies a customer-specific scrambling algorithm to the facility code bits within the PSK frame. The underlying modulation is still PSK at 125 kHz, and the raw bit count is unchanged, but the bit-order mapping of the facility code is rearranged according to a table that was defined when the original card order was placed. Readers programmed with that customer's FlexSecur profile expect data in the scrambled order; a standard Indala PSK card with an unscrambled facility code will be rejected.

The purpose of FlexSecur is to reduce the risk that a valid-looking credential from a different site will accidentally or intentionally present as valid on a different FlexSecur installation — since each customer's scramble order is unique. This is a site-level customisation layered on top of the PSK format, not a separate frequency technology. It is relevant for the Corporate 1000, FlexSecur and custom facility code guide because compatible Indala FlexSecur compatible cards require you to supply your existing scramble layout, which Security ID Systems uses to program each card to your facility's specific bit order.

Facilities that need to expand their FlexSecur installation should locate the scramble profile from either the original system integrator documentation or by submitting a sample credential for analysis. The scramble table is a customer asset; it is not derivable from reader hardware alone. This is the primary reason FlexSecur credentials require more information at the time of order than a standard Indala 26-bit or ASC 27-bit card.

Encoding a Compatible Indala Credential

All Indala PSK formats — including the 26-bit 40134, ASC 27-bit, 27-bit, 29-bit, Optus 34-bit, and DSX 33-bit — are encoded onto a T5577 substrate configured for PSK modulation. The programming process writes the facility code and card number into the appropriate bit fields for the target format, sets the T5577 configuration registers to PSK mode, and verifies the output waveform against the expected demodulator response. A correctly programmed card will present to an Indala reader identically to an original credential carrying the same credential data.

FlexSecur encoding adds a pre-processing step: the facility code bits are reordered according to the customer's scramble table before writing to the blank. The card number field is unaffected by the scramble. Cards produced with incorrect scramble data will be rejected at the reader, which is why supplying an accurate scramble profile is a prerequisite for order fulfilment rather than an optional detail.

For access control installations that span multiple panel brands — for example, a site using AMAG, Lenel, Kantech, or Keri panels with Indala readers — the encoding requirement is determined by the reader, not the panel. Panels from these manufacturers accept standard Wiegand data output from the reader, so as long as the credential is correctly encoded in Indala PSK, the panel receives valid Wiegand and operates normally.

Ordering Compatible Indala Cards and Key Fobs

The starting point for any Indala replacement order is confirming the exact format variant in use. The reader model number, original card part number, or system integrator documentation will identify whether the installation uses 26-bit 40134, ASC 27-bit, 29-bit, Optus 34-bit, DSX 33-bit, or FlexSecur. If documentation is unavailable, submitting a sample card for format identification is the most reliable approach — see the card format identification guide for the process. For facilities where the format is confirmed but the variant is ambiguous, a Indala 27-bit compatible prox card and a 26-bit card are not interchangeable, so verification before ordering avoids wasted stock.

Key fob versions of all standard Indala PSK formats are available through the compatible key fobs range, using the same T5577-based encoding on a clamshell or flat fob substrate. Fobs are ordered with the same credential data — facility code, card number range, and for FlexSecur, the scramble profile — as card credentials. There is no functional difference at the reader between a card and a fob carrying the same encoded data.

Bulk orders for property management, hospitality, and facilities management operations are quoted per project. For installations with multiple Indala variants across different reader generations — a common scenario in campus or multi-building environments — each variant is produced and labeled separately to prevent mix-ups at commissioning. 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 or Assa Abloy.