A wireless power transmitter (10, 600) that transmits power to a wireless power receiver (20, 700), the wireless power transmitter (10, 600) comprising: a wireless communication unit configured to communicate with the wireless power receiver (20, 700); and a controller, wherein: the wireless communication unit is configured to receive, from the wireless power receiver (20, 700), a first foreign object detection status packet and a second foreign object detection status packet, wherein the first foreign object detection status packet includes a first reference value that is one of a reference quality factor and a reference peak frequency, wherein the controller is configured to generate a foreign object detection indicator, indicating that a foreign object is present in a charging area of the wireless power transmitter (10, 600) characterized in that that the wireless communication unit is configured to transmit, to the wireless power receiver (20, 700), the foreign object detection indicator, that the second foreign object detection status packet includes a second reference value that is the other of the reference quality factor and the reference peak frequency, that the foreign object detection indicator is generated based on the first foreign object detection status packet and then the second foreign object detection status packet, that the first foreign object detection status packet further includes mode information indicating that the first reference value is included in the first foreign object detection status packet, and that the second foreign object detection status packet further includes mode information indicating that the second reference value is included in the second foreign object detection status packet. a wireless communication unit configured to communicate with the wireless power receiver (20, 700); and a controller, wherein: the wireless communication unit is configured to receive, from the wireless power receiver (20, 700), a first foreign object detection status packet and a second foreign object detection status packet, wherein the first foreign object detection status packet includes a first reference value that is one of a reference quality factor and a reference peak frequency, wherein the controller is configured to generate a foreign object detection indicator, indicating that a foreign object is present in a charging area of the wireless power transmitter (10, 600) characterized in that that the wireless communication unit is configured to transmit, to the wireless power receiver (20, 700), the foreign object detection indicator, that the second foreign object detection status packet includes a second reference value that is the other of the reference quality factor and the reference peak frequency, that the foreign object detection indicator is generated based on the first foreign object detection status packet and then the second foreign object detection status packet, that the first foreign object detection status packet further includes mode information indicating that the first reference value is included in the first foreign object detection status packet, and that the second foreign object detection status packet further includes mode information indicating that the second reference value is included in the second foreign object detection status packet. the wireless communication unit is configured to receive, from the wireless power receiver (20, 700), a first foreign object detection status packet and a second foreign object detection status packet, wherein the first foreign object detection status packet includes a first reference value that is one of a reference quality factor and a reference peak frequency, wherein the controller is configured to generate a foreign object detection indicator, indicating that a foreign object is present in a charging area of the wireless power transmitter (10, 600) characterized in that that the wireless communication unit is configured to transmit, to the wireless power receiver (20, 700), the foreign object detection indicator, that the second foreign object detection status packet includes a second reference value that is the other of the reference quality factor and the reference peak frequency, that the foreign object detection indicator is generated based on the first foreign object detection status packet and then the second foreign object detection status packet, that the first foreign object detection status packet further includes mode information indicating that the first reference value is included in the first foreign object detection status packet, and that the second foreign object detection status packet further includes mode information indicating that the second reference value is included in the second foreign object detection status packet.