A mobile key includes an RFID tag associated with a memory. The memory holds a secure access code. An authorization status for a person or item associated with the mobile key is determined by interrogating the mobile key using an RFID interrogation field. Security information, such as a secure identifier or access code, physical measurement data, or biometric data may be provided by the mobile key. The key may also comprise a wireless communication device, such as a cellular telephone. Security information, such as an access code, may be provided to the key using the wireless communication device or other communications network.