US Patent 11449691 Relay attack detection for interfaces using command-response pair

A reader device of an access control system comprises physical layer circuitry and processing circuitry. The processing circuitry is operatively coupled to the physical layer circuitry and is configured to initiate transmission of a command to a credential device; determine a time duration from sending the command to the credential device to receiving a response to the command from the credential device; and generate an indication when the time duration exceeds a relay attack detection threshold time duration.