A wireless power receiver , comprising: a wireless communication unit configured to communicate with a wireless power transmitter ; a memory configured to store a first reference value including one of a reference quality factor (Q_reference) and a reference peak frequency (F_reference_peak) of the wireless power receiver and to store a second reference value including the other of the reference quality factor (Q_reference) and the reference peak frequency (F_reference_peak); and a controller configured to transmit, via the wireless communication unit, a first foreign object detection status packet and a second foreign object detection status packet to the wireless power transmitter , wherein the first foreign object detection status packet includes the first reference value, wherein the second foreign object detection status packet includes the second reference value, characterized in that the controller is further configured to receive, via the wireless communication unit, a foreign object detection indicator indicating that a foreign object is present in a charging area of the wireless power transmitter , that the first foreign object detection status packet includes mode information indicating that the first reference value is included in the first foreign object detection status packet , that the second foreign object detection status packet includes mode information indicating that the second reference value is included in the second foreign object detection status packet , and that the foreign object detection indicator is determined based on the first foreign object detection status packet and then the second foreign object detection status packet . a wireless communication unit configured to communicate with a wireless power transmitter ; a memory configured to store a first reference value including one of a reference quality factor (Q_reference) and a reference peak frequency (F_reference_peak) of the wireless power receiver and to store a second reference value including the other of the reference quality factor (Q_reference) and the reference peak frequency (F_reference_peak); and a controller configured to transmit, via the wireless communication unit, a first foreign object detection status packet and a second foreign object detection status packet to the wireless power transmitter , wherein the first foreign object detection status packet includes the first reference value, wherein the second foreign object detection status packet includes the second reference value, characterized in that the controller is further configured to receive, via the wireless communication unit, a foreign object detection indicator indicating that a foreign object is present in a charging area of the wireless power transmitter , that the first foreign object detection status packet includes mode information indicating that the first reference value is included in the first foreign object detection status packet , that the second foreign object detection status packet includes mode information indicating that the second reference value is included in the second foreign object detection status packet , and that the foreign object detection indicator is determined based on the first foreign object detection status packet and then the second foreign object detection status packet . <EOS>