Wiegand wires are twisted into an “E” shape with two windings.

Wiegand Wire Cards (Figure 4.4) are access cards that use a series of short lengths of Wiegand wires embedded in it. These encode the identity of the card based upon the pattern of the embedded wires. The identity code of the wire is comprised of a combination of presence (wires present) and absence (wires absent) along the length of the card. A second set of wires provides a clock track against which the first set is compared. The card is read by swiping it through a slot in a Wiegand card reader that has a fixed magnetic field and a sensor coil. As each wire passes through the magnetic field its magnetic state flips, indicating a 1, and this is sensed by the coil. Where there is no wire, the number is registered as a 0. The Wiegand Protocol is a standard bit-code (typically 26 bits) comprising one parity bit, 8 bits of facility code, 16 bits of ID code, and a trailing bit for a total of 26 bits. The Wiegand protocol can achieve many permutations, including many specialized bit patterns, providing for a unique card for each individual facility.

Wiegand Wire Cards were extremely common for many years and presented the state of the art for non-proximity cards. Most Wiegand Card Readers were the swipe type.

The Wiegand Protocol provided for a significant advancement when it was introduced in access control systems in 1975, because it allowed for long cable runs from card readers (up to 500 feet). The typical Wiegand interface uses three wires, a common ground, and two data transmission wires usually called DATA0 and DATA1. When no data are sent, both are at high voltage. When a 0 is sent, the DATA0 wire is at low voltage while the DATA1 wire remains at high voltage. When a 1 is sent, the DATA1 is at low voltage while the DATA0 wire remains at high voltage. Most Wiegand protocols use a +5 volts DC to achieve the long cable runs. The Wiegand Protocol has also become the standard data protocol for Proximity type cards.

All of the cards we have discussed so far are either inserted into or swiped through a card reader. Proximity Cards are different. They are Radio Frequency Identification (RFID) cards that are read by placing the card near (in proximity with) a Proximity Card Reader. Proximity Card is the generic name for two types of these cards. It can refer to the older (125 KHz) or the newer (13.56 MHz) contactless RFID Cards.

Proximity Cards are tiny data transmitters that use no battery or energy storage device to operate. Instead, they do this by using resonant energy transfer. Proximity cards have three parts: a coil (antenna), a capacitor, and an Integrated Circuit (IC), which bears the ID code. The antenna of the card receives a radio frequency (RF) signal from the nearby card reader, which excites a coil and capacitor that are connected in parallel. The card reader presents an RF field that excites the coil (the antenna) and charges the capacitor. This energizes and powers the IC, which discharges its data code through the coil back to the card reader. The card reader transmits the card's code using the Wiegand Protocol (see the section Wiegand Wire Cards).

Active cards are typically used in long-range reader applications, most notably on toll roads and for vehicle or container tracking. Such cards have a battery inside that powers a more powerful Card ID transmitter.

125 KHz Proximity cards were a great advance over previous cards. 13.56 MHz tags were created in an effort to lower card costs and provide additional functions. In 13.56 MHz cards, the coil does not need to be made of hard copper wrappings. The coil can actually be a printed ink on a paper-like substrate that has an EEPROM added to it. During the mid- to late-1990s 13.56 MHz was the technology that many researchers thought could address very high tag usage applications such as library books, laundry identification, and access control. Typical tag costs run from 50 cents to $1.00. 13.56 MHz access cards often utilize so-called Smart Card technology, which enables read/write storage of data up to 64 MB per card. This also allows the cards to be used in cash management applications. 13.56 MHz cards can also be encrypted to reduce the possibility of their signal being intercepted and hacked.

Radio Frequency Identification Wireless Transmitter Systems are common in vehicle access control. These are usually configured similar to a garage door opener, but unlike a standard garage door opener, each individual unit has its own unique code it transmits to a receiver that converts this code to a card number using the Wiegand Protocol. The output of the receiver is connected to a card reader input on an access control panel, and the access control system operates the vehicle gate exactly as though a standard card were presented.

RFID Wireless Transmitter Systems are ideal where there is a high traffic area and a potential for a large queue to extend into a major road due to delays in presenting normal cards and the time it takes for the gate to open and re-close for each vehicle. It is common to see RFID Wireless Transmitter Systems used in high-end residential compounds.

As organizations grow, it is common for some employees to travel to multiple offices and facilities where different card technologies may be used. There are three solutions for this problem. One solution is to have the traveling employees carry a different card for each facility they visit. Another is to convert the entire organization's access control system to a single card standard, which can be expensive. Finally, technology can come to the rescue by creating a card that contains codes that are readable by two or more access control systems. Multi-technology cards can include Magnetic Stripe, Wiegand, 125 KHz Proximity, and/or 13.56 MHz Contactless Smart Cards all in one card, such as the one by HID Global Corporation.

Like Multi-Technology Cards, some organizations need to be able to read the cards of several facilities where different types of cards exist. One of the most common types of Multi-Technology Card Readers serves 125 KHz Proximity and 13.56 MHz Contactless Smart Cards. It is also common to see Proximity or Contactless plus a keypad all in one reader. In the past other Multi-Technology card readers existed, but they are rare today (Figure 4.5).

Access Cards grant access and Identification Cards provide visual evidence that the bearer is authorized to be in the area. Identification badges can have many visual attributes. These may include a photo of the bearer, a logo of the organization (not necessarily a wise thing), the bearer's name, a color scheme that may identify areas where the person is authorized, and sometimes a color or code may designate if the bearer is a contractor or vendor.

To help verify the authenticity of the card, it is common to laminate a holographic overlay, which provides a visual indication that the card has not been tampered with. Some organizations use a separate access card and identification card, but most have combined the two functions together into a single credential (Figure 4.9). These are printed on a Photo ID card printer (Figure 4.10).