How Proximity Cards Work

A Complete Guide to Proximity & Smart Cards

What Is a Proximity Card?

A proximity card (often called a prox card) is a contactless access card that can be read without inserting or swiping it through a reader. As long as the card is within close range of the reader, it can securely transmit its data and grant access—making it fast, convenient, and reliable.

Because proximity cards do not require physical contact, they can stay inside a wallet or purse and still function properly.

Most proximity cards look like standard 30 mil PVC ID cards, but inside they contain an embedded metallic antenna coil and microchip that store encoded data. In addition to traditional card formats, proximity credentials are also available as:

• Clamshell cards
• Key fobs
• Adhesive stickers

How Do Proximity Cards Work?

Proximity cards operate using low-frequency radio waves, typically 125 kHz.

Here’s what happens when a proximity card is used:

1. The access reader emits a low-frequency radio signal
2. When the card comes within range, the antenna inside the card is energized
3. The card transmits its unique identification number to the reader
4. The reader sends that number to the access control panel
5. The system checks the number against its internal database
6. If the number is authorized, the door unlocks

This entire process takes less than a second—providing seamless, secure access without physical wear on cards or readers.

The Technology Behind Proximity Cards

Bit Formats Explained

Proximity cards use different bit formats to structure the data stored on the card. Common formats include:

• 26-bit (industry standard / Wiegand)
• 32-bit
• 34-bit
• 35-bit
• Up to 40-bit

26-bit Wiegand is the most widely used open format and works with the majority of access control systems.

Other formats are often brand-specific or “closed” formats. While these may sound more secure, they typically offer no additional protection and are primarily used to lock customers into proprietary card purchasing.

What’s Encoded on a Proximity Card?

A typical proximity card number is made up of four components:

1. Parity Bits

Parity bits appear at the beginning and end of the data string. Their role is simple: error detection. You don’t need to manage these directly—they’re built into the encoding process.

2. Facility Code

The facility code identifies your location or system. It is usually a number between 1 and 255 and helps keep card credentials unique across different buildings or organizations.

Each site typically has its own facility code, especially in multi-location environments.

3. Card Number

This is the unique number assigned to each individual card. Most systems start at card number #1 and increase sequentially as new cards are issued.

⚠️ Important: Card numbers must never overlap. If two cards share the same number, the access system will treat them as the same card.

Proximity Card Encoding Example

(Insert visual diagram or encoding example here if desired.)

How to Order Additional Proximity Cards

When it’s time to order more cards, you’ll need the following four pieces of information, all of which can usually be found in your access control panel:

1. Bit Format
   1. Most commonly 26-bit
   2. Can range between 24–40 bits
2. Card Type
   1. Often printed directly on the card
   2. Also viewable in your control panel
3. Facility Code
   1. Each building typically uses a different one
   2. Verify carefully if you manage multiple locations
4. New Card Number Range
   1. Example:
      1. Last issued card: #7283
      2. Ordering 1,000 more cards
      3. New range: #7284 – #8283

✅ Always double-check that the new card range does not overlap existing cards.

Helpful Notes Before You Order

Note 1:
Any proximity card type—cards, fobs, or stickers—can be encoded to match your existing format. This means you can mix credentials without changing your system.

Note 2:
Can’t find your system information? Send us a working card, and we’ll read the data and extract everything needed to place your order accurately.

Note 3:
While HID is the most well-known brand, many other manufacturers offer fully compatible proximity cards—often at a better price. Even if your system uses HID, alternative brands can work perfectly and may qualify for a 100% money-back guarantee.

Pro Tip: Printing on Proximity Cards

If you plan to print photos, logos, or color designs on proximity cards, we strongly recommend using a retransfer printer instead of a direct-to-card printer.

Retransfer printing delivers:

• Sharper image clarity
• More vibrant colors
• Improved durability
• Better results on embedded electronics

We’re Here to Help

Our ID System Specialists are available to guide you through every step—from identifying your card format to placing your order with confidence.

📞 Call us at 866-438-4553
You'll always reach a live expert, ready to help.