Wireless charging systems for electronic devices

Embodiments describe a portable electronic device that includes a housing having an interface surface and an inductor coil disposed within the housing and comprising a conductive wire wound in a plurality of turns about a center point and in increasing radii such that the inductor coil is substantially planar. The portable electronic device further includes charging circuitry coupled to the inductor coil and configured to operate the inductor coil to wirelessly receive power and wirelessly transmit power, control circuitry coupled to the charging circuitry and configured to instruct the charging circuitry to operate the inductor coil to wirelessly receive power and to wirelessly transmit power, and a device detection coil coupled to the control circuitry and configured to detect the presence of an external device on the charging surface, the device detection coil is configured to operate at a different frequency from the inductor coil.