40-bit is the length of the Wiegand number.
If the site already uses another bit length, stay on that format or re-issue cards and reprogram the panel together.
40-bit Wiegand
A 40-bit Wiegand card format. Cards, reader, and panel must share this length.
Also called
40-bit40 bit Wiegand40-bit Wiegandwiegand bits 40 bit
Catalog fields
Wiegand Bits
Source: Transmitter Solutions product training