A primary device for inductive power transfer to a secondary device , the primary device comprising: I) a primary coil , the primary device being configured to i) operate in a first mode during which the primary coil transfers power through inductive coupling to the secondary device and a load is connected to the secondary device , the secondary device being configured to supply the transferred power to the load , and ii) operate in a second mode during which the load is disconnected from the secondary device and a foreign object is detected; and II) a primary controller configured to operate the primary coil i) using a first frequency (f1) during the first mode while the load is connected to the secondary device , and ii) using a second frequency (f2) during the second mode while the load is disconnected from the secondary device ; III) wherein the primary device is configured to measure a primary current (I) in the primary device while the primary coil is being operated at the second frequency (f2) during the second mode to detect presence or absence of a foreign object , and IV) wherein the second frequency corresponds to an operating frequency at which the primary current does not vary with respect to an air gap between the primary coil and a secondary coil of the secondary device ; V) wherein the second frequency (f2) corresponds to a point (P) where a first current curve corresponding to a minimum air gap between the primary device and the secondary device meets a second current curve corresponding to a maximum air gap between the primary device and the secondary device , the point (P) being a meeting point at a frequency larger than the frequencies at which the maximum in the first and second current curves occurs. I) a primary coil , the primary device being configured to i) operate in a first mode during which the primary coil transfers power through inductive coupling to the secondary device and a load is connected to the secondary device , the secondary device being configured to supply the transferred power to the load , and ii) operate in a second mode during which the load is disconnected from the secondary device and a foreign object is detected; and II) a primary controller configured to operate the primary coil i) using a first frequency (f1) during the first mode while the load is connected to the secondary device , and ii) using a second frequency (f2) during the second mode while the load is disconnected from the secondary device ; III) wherein the primary device is configured to measure a primary current (I) in the primary device while the primary coil is being operated at the second frequency (f2) during the second mode to detect presence or absence of a foreign object , and IV) wherein the second frequency corresponds to an operating frequency at which the primary current does not vary with respect to an air gap between the primary coil and a secondary coil of the secondary device ; V) wherein the second frequency (f2) corresponds to a point (P) where a first current curve corresponding to a minimum air gap between the primary device and the secondary device meets a second current curve corresponding to a maximum air gap between the primary device and the secondary device , the point (P) being a meeting point at a frequency larger than the frequencies at which the maximum in the first and second current curves occurs. <EOS>