An access-control reader is hardware installed at an entry point that detects and checks a presented credential, such as a plastic card or a mobile credential sent over NFC or Bluetooth Low Energy. It communicates with an access-control system, which determines whether access should be granted and signals the door hardware accordingly. The reader may pass credential data to a separate controller rather than make the final decision itself.
Readers matter because they connect credentials to physical access. In attacks, tampering with or exploiting a reader, its communications, or an unsupported legacy configuration can undermine access controls. In defenses, organizations should inventory reader models, verify compatibility before adding mobile credentials, and protect reader-to-controller communications. They should also test revocation, fallback credentials, and failure behavior so that a lost phone or system outage does not leave access unmanaged.