The Wiegand Effect: How a Musician-Turned-Engineer Transformed Access Control

In the 1930s, John R. Wiegand left Germany for New York City, drawn not by science or engineering—but by music. He came to study piano and choral conducting at the world-renowned Juilliard School. But fate had other plans. While he would later become an engineer, it was his perfect pitch—the rare ability to identify musical notes without reference—that gave him a unique advantage in an entirely different field: magnetics. This unusual talent would ultimately lead to a groundbreaking discovery in the early 1970s—the Wiegand Effect—a phenomenon that would quietly revolutionize the access control industry.

What Is the Wiegand Effect?

In 1974, John Wiegand patented a unique type of wire now known as Wiegand wire. This wire is crafted from a specially treated iron alloy with a hard magnetic outer shell and a soft magnetic inner core. When the wire is exposed to a changing magnetic field, something unusual happens:

1 The outer shell magnetizes quickly and saturates.

2 Then the inner core starts to magnetize.

3 Suddenly, the entire wire flips polarity—creating a sharp voltage pulse.

These voltage pulses are easy to detect and are the key signals used in Wiegand-based systems. The behavior of the wire is completely bistable, meaning it switches between two states in a predictable and reliable way, ideal for digital signal generation.

Turning Wires into Access Cards

In the late 1970s, Wiegand, along with his business partner Milton Velinsky, took this effect a step further. They embedded rows of Wiegand wires into plastic cards—each row representing a binary data line (D0 for Data Zero and D1 for Data One). As the card passed over a magnetic reader, the wires produced distinct pulses that translated into a sequence of 1s and 0s—a binary ID.

This innovation led to the creation of Wiegand cards and the Wiegand interface, which soon became the industry standard for transmitting access control data.

At the time, these cards had two major advantages over magnetic stripe cards:

They couldn’t be re-written.

They were hard to counterfeit due to the difficulty of embedding and aligning Wiegand wires.

The Wiegand Interface Lives On

Even though actual Wiegand wire cards are rarely used today, the Wiegand interface—that two-wire D0/D1 signal method—remains a core part of the access control world.

Modern access cards like Proximity (Prox), MIFARE, and iCLASS still rely on Wiegand-format output to transmit data from the card reader to the access control panel. This format is simply a set of binary bits sent over two wires. The most common format historically has been the 26-bit Wiegand, with 8 bits for the facility code and 16 for the user ID. Some government systems now use formats as long as 200 bits.

Still Undefeated After 50 Years

Though newer technologies have emerged—like encrypted smart cards and mobile credentials—the Wiegand interface isn’t going anywhere soon. It’s deeply embedded across access control systems worldwide, and its simplicity, reliability, and legacy support keep it in wide use.

What started as a curious observation by a musician with perfect pitch has become one of the most resilient foundations in electronic security.

John R. Wiegand didn’t just discover a neat magnetic trick—he unknowingly rewrote the blueprint for secure access technology. And nearly half a century later, his invention continues to quietly unlock doors around the world.

Are you looking to develop an interface using access control formats, Wiegand compatibility, or upgrading legacy systems? Let me know—I’d love to help you explore the tech that’s keeping buildings secure today.