Access badge

An access badge is a credential used to gain entry to an area having automated access control entry points. Entry points may be doors, turnstiles, parking gates or other barriers.

Access badges use various technologies to identify the holder of the badge to an access control system. The most common technologies are magnetic stripe, proximity, barcode, smart cards and various biometric devices. The magnetic strip ID card was invented by Forrest Parry in 1960.

The access badge contains a number that is read by a card reader. The number is sent to an access control system, a computer system that makes access control decisions based on information about the credential. If the credential is included in an access control list, the access control system unlocks the controlled access point. The transaction is stored in the system for later retrieval; reports may be generated that reveal who entered what controlled access point at what time.

The Wiegand effect was used in early access cards. This method was abandoned in favor of other proximity technologies. The new technologies retained the Wiegand upstream data so that the new readers were compatible with old systems. Readers are still called Wiegand but no longer use the Wiegand effect. A Wiegand reader radiates a 1" to 5" electrical field around itself. Cards use a simple LC circuit. When a card is presented to the reader, the reader's electrical field excites a coil in the card. The coil charges a capacitor and in turn powers an integrated circuit. The integrated circuit outputs the card number to the coil which transmits it to the reader. The transmission of the card number happens in the clear—it is not encrypted. With basic understanding of radio technology and of card formats, Wiegand proximity cards can be hacked.