# HID ADT 31bit

Everything you need to understand HID ADT 31bit

## Card format Overview

A proprietary 31-bit card format used in access control systems, featuring a unique structure composed of 4-bit site code and 23-bit card number, allowing for easy management and avoiding card number duplication for secure, contactless access.

## HID ADT 31bit format properties

### Site Code

4 bits. The facility code range is 0 to 15.

### Card Number

23 bits. A unique serial number (0-8,388,607) for each card within that facility code.

### Generate examples

Put in the values for this card format, we'll generate the results in a few different formats.

#### Here's your example

| Format | Value |
| --- | --- |
| Hex | 3C000320<br>Copy |
| Decimal | 1006633760<br>Copy |
| Binary | 0111100000000000000001100100000<br>Copy |

## The API that turns phones into key fobs.